All pictures Samantha Hayley

A couple of weeks before the election, a Conservative campaign poster appeared on the billboard by the main road, round the corner from my flat. It boasted of the strength of the economy. It was on the side wall of a shop which had closed down; the doorway was stuffed with a sleeping bag and a couple of cardboard boxes. I looked up at the poster and I laughed out loud. Why were they wasting their money? Nobody round here votes Tory.

Then one Friday I was walking down the hill, heading in the opposite direction – literally and figuratively – to the usual snake of rush hour traffic, and it dawned on me. The poster wasn't there for us. Of course it wasn't. It was for commuters, heading out of London with their windows wound up tight, towards the sloping lawns and sweet, sweet leaves of Hertfordshire. It was in our space, without acknowledging our presence – sort of like the Evening Standard. I had to walk underneath it every day.

For years, Jeremy Corbyn was my local MP. I voted for him cheerfully. One of those beardy, tea-drinking lefties – just what you want at constituency level. I was dimly aware that he was said to hold some colourful opinions here and there, on this and that; none had any bearing on the parliamentary representation of our slightly grubby London suburb.

(Things are different now.)

But if you'd asked me, back in the day, how I felt about Jeremy Corbyn becoming the leader of the Labour Party, I'd have chuckled softly, shaken my head, realised that you meant the question seriously, doubled the size of my eyes, exhaled through a pursed-up mouth, then finally said “Hmmmmmmm. I like what that question implies. I really do. But does it absolutely have to be him?”

(Some things haven't changed.)

We're now three days away from the result of the Labour leadership election, and as you may or may not have heard, Jeremy Corbyn is the runaway favourite.

There's a sense in which all this is bloody marvellous. Well-heeled columnists and dinner-party commentators, let alone the moribund Labour Right, have no idea how desperate the situation has become. Corbyn's supporters – even the worst of them – understand it all too well. This, in many cases, will be why they are prepared to overlook the things they overlook. All that hope and anger, all that deep frustrated longing for something good, projected onto those snow-white whiskers...

And then there's a sense in which all this is bloody petrifying. Jeremy Corbyn? Are you fucking serious?

Does it absolutely have to be him?

On the train to Chelmsford, heading towards a Jeremy Corbyn campaign rally, I sit across from a businessman with a beard down to his tits.

Outside all the windows are these empty new buildings, flaring in the afternoon sun; impossible towers, fairy-tale money-pots, make-believe homes for make-believe people. In our space, without acknowledging our presence. I'm staring down at an ancient mobile phone, drinking a paper cup of awful coffee – I'm part of the modern world. Out past Stratford, Romford, Brentwood. Tiny rooftops, dirty, peeping out from behind the scaffolding.

Then suddenly everything opens out, and we're speeding through the Essex countryside. Late afternoon easing into early evening. Late summer easing into early autumn. Contrails are dissolving in the sky; people coming and going. The sunset, melting. Everywhere's green. Through the open windows drifts the sickly, overwhelming smell of manure.

Whenever Labour need to elect a leader, a left-wing candidate stands. Everyone knows that they're going to come last, but it makes the party feel good about itself; it's a way to connect with, contain and cosify the past. It's like one of those folksy old traditions that you get in Dorset – every Maundy Thursday everyone gathers at the mill pond and hurls bindweed at the seventh oldest virgin in the village, who's dressed up in a suit of peas. (His name is Bobbly Jack.) It's a novelty, isn't it? It's a bit of fun.

(But things are different now.)

The ceiling's caved in on New Labour. Bits of plaster had been coming down since well before the last election, but everything collapsed when Harriet Harman, interim leader, tried to get around the trap the Tories had set with the welfare bill – a trap as clear as fear – and plumped for what she seemed to think was a clever compromise: abstention, en masse.

But this happened instead.

Now just because Tony Blair says something, doesn't mean it can't be true. Blair's “interventions” in the run up to this vote have been drowned out, unsurprisingly, by a heavy chorus of boos. But while Blair was only half-right when he linked the “Corbyn surge” not just to Syriza and Podemos, but to the likes of UKIP and Marine Le Pen, he was correct to be concerned about the somewhat unstable, rudderless nature of this “vast wave of feeling against the unfairness of globalisation, against elites”. Of course, if he had not worked quite so tirelessly to reshape Labour into a party which would reinforce that “unfairness” and pander to those “elites”, there might not be this sense of desperation in the first place. People would be less inclined to seize onto the first thing that floats by, and not let go.

But he did, and now they do. Many Labour voters feel that they've already tried a “moderate” and “plausible” alternative. Everyone knew Ed Miliband was basically a decent man, but a lousy, de-electrifying leader. Some collective desperation kept the Labour faithful hoping, but that 10 o'clock exit poll which hit like a thunderclap... once the room stopped shaking, it was hard not to feel, somehow, we'd known it all along.

(Thanks for everything, Ed. I'll never forget you. And one day I'll be in a pub quiz somewhere, and that'll earn me a point.)

But now that this desperation has deepened, people will believe still stranger things. Some of Corbyn's fans have even managed to convince themselves the Right are scared of him – “Ooh, he's got them rattled!” – when they are in fact bouncing up and down on their beds and whooping. It's likely that a Corbyn-led Labour Party, tanking in the polls, would create space for the Tories to reach that bit further, cut that bit deeper, since there would now be – quite literally – No Alternative. This scenario does not “frighten” the Right, nor does it appear to greatly concern the Corbyn massive. But it scares the hell out of me.

(Which is why I don't entirely hold with these folk who go on about purity in opposition... They're not the ones who are going to be homeless this winter. Oh, didn't I mention that? I shan't bore you with it.)

The fact is, unless a lot of things change deeply and most unexpectedly over the next four years, Jeremy Corbyn is not going to win a general election. This is not to suggest that there's some kind of objective, immovable “centre ground”, nor that if there were, it would be occupied by the Labour Right – still less the modern Conservative Party. In truth, Corbyn's domestic policies are not very extreme, and would in many cases prove quite popular. Yes, they're “radical” in the sense that there's a chasmal distance out to there from where we are today, but really, Corbynism is just about hauling Britain back towards the social-democratic Centre. There will be no pogroms, no fifteen-hour queues for stale bread. This is not the problem.

I think we all know what the problems are. For instance, I'm not what you'd call a hawk, but please: out there in grainy, hard-bollocked reality, Corbyn's foreign policy would not just leave Britain naked in the conference chamber, but fastened into a gimp mask with a horse-tail dangling out of its arse. Whether we like it or not, there is at least one confrontation coming; you can be sure of that. There are some nasty people in the world, you know. Some of them – get this! – are even nastier than Tony Blair. And even if you leave them all alone, they will not stop. Not for all the tea in Islington North.

What's more, there are certain... issues with Corbyn and the company he keeps. He doesn't just have skeletons in his closet, he hangs up his shirts in an ossuary. This is not a trivial matter. Those who underestimate the problems this will cause are fooling themselves (and in some cases, losing sight of their own moral compass).

Don't get me wrong. My desire for a Left or leftish alternative to permanent austerity is so strong that I could weigh all these things up and still decide that yes, a Corbyn government is something I could vote for – albeit with my mouth in the shape of a wavy line and a hand to my brow. But let's not fantasise. Most British voters will respond to Corbyn much as they'd respond to a man weighing five stone five, with blood trickling out of his left ear, asking for a loan. The very phrase “a Corbyn government” has a whiff of pixie dust about it, something chimerical. This doesn't worry the Corbyn faithful.

We have no choice, they say. This is the last roll of the dice.

Well, I have two worries. Firstly, we're going to sea in a sieve. The rebuilding of the Labour Left, not just as a force within the party but as something which could make a realistic bid for government, is a massive project which requires meticulous planning, a lot of patience and probably a genius at the helm. What's more, I'd say that Labour only gets one shot at this, and has to get it absolutely right first time. There are no half measures, either: those who make half a revolution dig their graves. This suggestion – well, it's more than a suggestion, I suppose – that we should do this now, entirely on the hoof, with a hostile party, a makeshift leader and nothing approaching a power base...

My second worry is... this is the last roll of the dice.

Time is short. Stare into the bleakness of the future as it stands: TTIP, corporate rule, maximum secrecy, minimum privacy, elimination of workers' rights, a cultural vacuum, no education, dead suns and collapsing horizons... Goodbye to the NHS, goodbye to the welfare state. Goodbye to everything. Just goodbye.

And yet, and yet... the cold reality of casting a vote for Yvette Cooper, her exciting plans for cutting corporation tax, her benefits crackdown...

Yet again the Left is in a corner, driven there not just by slick manoeuvring from the Right, but by its own persistent stupidity. The fact is, this leadership election could end up enabling a de facto right-wing one-party state... either because Labour is too timid, or because it is too bold.

So, I made it to Essex. The heartland of working class Conservatism; the Agincourt of Thatcherism. At the last election the Tories took 51% of the vote in Chelmsford – nearly three times as many suckers as Labour. Since 2010, the UKIP vote has increased sevenfold; they were only a polling-day rainstorm from beating Labour back into third. This is not Corbyn territory. Five hundred people are out tonight – that looks like a lot of vote-meat when it's lined up down a sidestreet (four hundred and ninety-six more than you'd get at the Andy Burnham Roadshow), but it's not quite revolution yet.

Outside Chelmsford Civic Theatre – the kind of council-run arts venue which won't exist in ten years' time, if things go on the way they are – representatives of various far-left factions hang around, ants at a picnic, opportunistic, doing the things they do. These are the terrifying “entryists” we've been hearing so much about, an army of hard-left activists who tend to gather in groups of twenty or thirty in the upstairs rooms of pubs – a ruse to conceal their true numbers, no doubt – and who've now put aside a century's worth of livid but incomprehensible sectarian feuds in order to come together and pervert the course of bourgeois democracy. Over there, an old lady from the Communist League is selling books from a fold-up picnic table. It would appear that demand for Thomas Sankara Speaks: The Burkina Faso Revolution 1983-87 is just a little slack. Over here, a woman with a fading American accent tries to sell me a copy of Workers Hammer, apostrophe-shy newspaper of the Spartacist League of Britain.

“Do you want to buy our newspaper? It's only 50p.”

“Which tendency are you, then?”

“Trotskyist.”

“That doesn't really narrow it down.”

I glance at the cover: oh right, it's the Sparts. I wonder who on Earth is paying to keep all these papers in print these days, now that most of the great 20th century human rights abusers are dead.

“It offers a Marxist perspective on world events,” she says. “Would you be interested?”

“Well,” I say. “I am a Marxist. But in terms of a system of thought, you know, not so much at the ballot box, because...”

Her expression hardens suddenly.

“I don't think it's about the ballot box.”

I can only shrug. “I'm a pragmatist.”

“So am I!” she snaps back sharply. “That's why I'm for revolution!”

What a salesperson. Dear old Sparts... don't ever change (the last I heard, they'd declared solidarity with ISIS, who must have been thrilled to hear that). I take a copy anyway – for research, let's say – and stuff it into my shoulder bag, already overflowing with leaflets and Mentos chewing gum and glossy red pamphlets with Jeremy Corbyn's face on, covered with quotes from Charlotte Church.

I step inside – some bungler's left my name off the press list, but they take pity on me, and let me in anyway. If ever you wanted to illustrate the best and worst aspects of the British Left...

In the auditorium, the crowd is pretty much as I expected. The average age is probably fifty, but there are almost no fifty-year-olds: mostly, it's the under-30s and the over-60s. Snow-topped grizzlers, veterans of those great defeats of the 1980s, and a bunch of clean young people who can be bothered to give a toss. Lots of them in T-shirts with words on: “100% Socialist.” “Never Trust A Tory.” Someone's brought a packet of chicken caesar wraps from Tesco's and is sharing them out with their mate. Inevitably, someone else has brought their kids (stoked, no doubt, at the prospect of a 15-minute speech by Roger McKenzie, assistant general secretary of Unison).

Young volunteers in hi-vis jackets are acting as stewards, wandering up and down the aisles. One is the absolute spit of Roxy Jezel – if you don't know who that is, you're a better man than I – and I'm ashamed to say I do a double take before it dawns on me that... nah, it probably won't be her. A man with a megaphone tries to tell the crowd that someone's dropped their wallet, but his megaphone has broken.

“I've got some spare batteries,” shouts another steward on the other side of the hall, hand cupped to his mouth.

“I just put in some new ones,” the first bloke calls back.

“Oh, right,” bellows his mate. “You're better off shouting, then.”

In the end, some imbecile with a giant beard and a man-bun goes round doing the shouting – and during the daydream that follows I realise that nobody's searched my bag. Not that it matters much: I'd imagine that Corbyn's enemies are quite relaxed in the expectation that he'll become his own Sirhan Sirhan.

The smell of chicken caesar wraps drifts over to where I'm sat, which is as close to the back of the hall as I can get. The rally's sold out, but some folks haven't been able to make it because of a traffic jam near Chingford, so I move over into the seat on my right. I couldn't see a thing before. The lad in front of me's wearing a massive baseball cap with “REVOLUTION” printed on it. It was blocking my view.

There was a phrase you used to hear in the Cold War days, if you spent enough time around penitent ex-communists: “What was your Kronstadt?”

This is a reference to the Kronstadt Rebellion of 1921, when Russian sailors and peasants, most of them veterans of the revolution, rose up in protest at Bolshevik rule, demanding something less repressive, something more like what they'd been fighting for. Instead, over the next few weeks they were slaughtered in their thousands by the Red Army – this is where the revolution first embraced state terror (an embrace which can never be broken). “What was your Kronstadt?” meant “When did you finally accept that you could no longer support, or make apologies for, the Soviet Union?” Sixties radicals spoke of the tanks in Budapest and Prague; others had already thrown in the towel, with the post-war annexation of the eastern European states. For one or two rather more senior comrades, Kronstadt was their Kronstadt.

It would be grandiose to draw a direct parallel, but still, it makes me think of what went down with me and the Mainstream Radical Left. Not that I was ever all that active in the struggle. This was partly laziness, partly an antipathy to dogma, but also, if I'm being honest, I just couldn't stand those bloody people and didn't want to spend any time with them. But you know... solidarity, right? I'd stick up for the Left like a drunken brother, because I wanted the best for it, because I wanted the other guys to lose... and because my heart was in it, somewhere. This is what I think, it's how I think; it's what I am. And nobody wins who fights alone.

I remember feeling quite uncomfortable with some of what was going round in the aftermath of 9/11, but the Left is a broad church, and has never wanted for ghouls and blockheads. I put it out of my mind. But things got worse around the time of the war in Iraq: I was against the war just like everyone else I knew, but deeply unimpressed by many of the loudest voices in the anti-war movement, whose desperate attempts to close down all debate seemed shrill and foolish, not least when – too often the case – their own views were fatuous and rather ill-informed. And, while I opposed the war, I still hoped something good might come of it, somehow. Clearly not that creepy neo-con pipe-dream with the children waving the Stars and Stripes and singing songs about Donald Rumsfeld, but possibly a functioning democracy, the final defeat of Ba'athism, some kind of bulwark against radical Islam... no, I wasn't hopeful (lack of faith in all of this was partly why I hadn't backed the war), but still, I was hoping. Yet I couldn't help noticing how many on the Left were cheering on what they called “the insurgency”, nor how sharp they soon became with those who wouldn't join them.

Around this time, the Stop The War Coalition, of which Jeremy Corbyn was – and still remains – the national chair, praised the “legitimacy” of the Iraqi resistance (in truth, a ragged band of Ba'athist remnants and Al-Qaeda In Mesopotamia), and expressed support for their attempts to fight the occupation “by whatever means they find necessary”. In other words, now that the bombs had fallen, they were quite determined it should all have been for nothing. Iraq had been the property of Saddam Hussein for 24 years, had been half-starved by sanctions and shattered by the 101st Airborne; still, it seemed, this wasn't enough. Iraqis must now live in an insoluble and bloody chaos, under the heel of petty thugs and theocratic terrorists, just in case they accidently made George W Bush look good. Back then – before all hope dissolved – most Iraqis did not share this view. But to the Mainstream Radical Left, it didn't really matter what Iraqis thought or wanted. This was a point of principle.

For ten years I listened to rubbish like this, on all kinds of subjects, reassuring myself these people were just a small but noisy minority... even when it became quite clear that this was no longer the case.

In the end, my Kronstadt came on the 7th of January 2015, when fascists forced their way into the office of a small-circulation satirical paper and killed twelve people, many of them long-time Leftists, lifelong supporters of anti-racist, anti-fascist causes; tireless tormentors of the Right in all its forms. And almost instantly, the Mainstream Radical Left – from a position of near-total ignorance as to what this Charlie Hebdo even was – began to slander the dead, announcing to no one in particular that they were not going to cry for them... before their bodies were even cold. Were not those caricatures of thick-lipped Africans and big-nosed Arabs transparently racist? Well, they didn't look great, it's true – but the intent and the actual meaning of those Charlie Hebdo covers which were flashed around the globe had been entirely lost in (non-) translation. In vain did the rest of us explain that all this ire had been misplaced, and anyway, none of these people were killed for being “racist” – they were killed for being blasphemous. That was the whole of the point. And if you could not or would not understand that, you were never going to understand a thing about these murders, or begin to grasp their true significance. Still, the arguments kept going round and round. Nothing could shake the Mainstream Radical Left's determination to indulge Islamic radicalism, even as its self-appointed warriors cut their comrades down. Truly, the anti-imperialism of fools.

(Stop The War ran several pieces on their website relating to the Charlie Hebdo murders. They're still there, if you want to read them. “It is a great testament to the enduring humanism of the Muslim population of the world,” says one, “that only a tiny minority resort to such acts in the face of endless provocation.” Well, that's one way of looking at it.)

So it was time to make a choice. Did I want to make excuses – even in my own mind – for a version of the Left which laughed at murdered soixante-huitards and stopped short of cheering their fascist killers – as they'd cheered for fascist killers elsewhere – only because Paris was a bit too close for comfort?

Sure, disengaging wasn't a complex procedure, seeing as I wasn't really that engaged in the first place. There were no forms to fill in, no phone calls to make. But you know, it's the thought that counts. No, really – it's the thought that counts. Because for as long as people let this dangerous stupidity go by, in the name of solidarity – or something – it just keeps on growing. Quietly it creeps, until it becomes an orthodoxy, received wisdom, an article of faith. And then, God help us, the next thing you know, the Labour Party elects a leader who gives this bullshit house room. And then you have to vote for it.

Jeremy Corbyn may well be significantly smarter than most of these people – or he may not. The point is, he's their man, their voice, their representative.

I've been waiting most of my life for the Left to make its glorious return. This is not what I've been waiting for. I've not changed my principles, and have only changed my views to fit the facts. I'm the one who feels abandoned – everything has moved around me. I lay down in a big tent, and I woke up in the rain.

Up on stage there's a long low table, and behind that there are several bright red boards with Corbyn's logo on them. It looks like the logo of an outsourcing firm, or a local radio station. There's a camera on stage pointing into the crowd, and at random intervals the flash goes off. Even back here, it's blinding. Every time, it feels like a kick in the eyes.

The chairman tonight is a genial Geordie trade unionist. “Jeremy spoke at an event in Colchester earlier,” he warns us, “so not to put too fine a point on it, the man's completely whacked!” (Yeah, that sounds like a punishing schedule – good job he's not running for Prime Minister or anything.) There are pantomime boos and hisses whenever he mentions Tony Blair, and then a spontaneous round of applause when he mentions Tony Benn. Once we've listened to Kelvin Hopkins, Labour MP for Luton, who is bald and jolly and looks like a baker, Geordie comes back on and tries to make a point about something or other, but halfway through his second sentence Jeremy Corbyn shuffles onto the stage behind him, staring at the floor, and gets an instant, clattering, foot-stamping ovation. That's called being upstaged. Poor Geordie! The camera flashes in my eyes, again.

But it's like a soul revue – we're made to wait for the main attraction. Next on the bill is Tony Kearns, deputy general secretary of the Communication Workers Union (his page on the CWU website proudly boasts that “Tony is not a member of the Labour Party”). He turns out to be a likeable Scouser who wakes the audience up with his opening words – “Hiya!” - then speaks at considerable length about the privatisation of the Royal Mail. I agree with every word he says; I suspect that the crowd do, too. But time is passing slowly. Corbyn sits there, rubbing his eyes, idly scribbling notes. It's all a bit like a boring night in the pub, except that you can't join in. The arguments are sound, but they're mostly very simple.

And it goes on. Shelly Asquith, vice-president of the NUS, an impeccably-groomed young blonde woman sat among tired-looking men of a certain age – it looks a bit like Sky Sports News on transfer deadline day – explains that Corbyn is the only one of the leadership candidates who's been consistently pro-migrant (a ripple of applause), pro-free education (she really belts this out, but to a fairly muted response) and anti-interventionist (instantly, the hall erupts with cheers). I wonder about priorities... but then all thoughts are blasted out of my head by Roger McKenzie, assistant general secretary of Unison. Within seconds of beginning his speech he's screaming his head off, blowing the lights out, voice shaking with uncontrolled emotion, as though this were a frosty night on the Govan shipyards rather than the here and now, with most of the crowd – who look like they're here to see Vampire Weekend – just staring back at him blankly, one or two of them nibbling away on Tesco's chicken caesar wraps.

But then something happens, and it catches me off-guard. Reaching the end of a long, long litany of basic Labour values, he adds “... and for the first time, I'm saying these things and not wondering whether the person next to me, standing for Labour leader, is going to support them.”

And he's right, you know.

The flash goes off in my face again. I think it's giving me a sinus headache.

Assuming he comes out on top this Saturday, the media assault on Jeremy Corbyn will barely have begun. What we've heard so far is just a clearing of the throat.

Of course, a lot of it's pure hysteria, the same old junk that's hurled at every lefty who breaks cover: he's mad, he's weird, he wants to force us all to dress in boiler suits and only eat potatoes. A lot of it involves the twisting of his words until they squeak – e.g. the flagrant misreporting of some cautious and equivocal comments re. segregated carriages on late night trains. But much of it is not hysteria. Much of it has not been twisted. Much of it is simply reportage; the startling facts. Incredulous hacks, digging not-very-deep, have uncovered a seam of words and deeds so appallingly and astonishingly ill-judged, they cannot believe their luck. Do not doubt that there will be a whole lot more of this. Corbynites' attempts to wave this stuff away, as though it were just tittle-tattle, are foolish indeed (and in some cases, shameful). This stuff is incredibly worrying – both in terms of what it says about the man behind the beard, and in terms of what it means for the future of the Labour Party, specifically the Labour Left. And by extension, the future of Britain.

We needn't go through all the details again. Everyone's aware by now that Corbyn has referred to members of Hamas and Hezbollah as “friends”, that he's courted and supported all kinds of anti-semitic nutbags and babbling enthusiasts for jihad, then defended them in robust terms when asked what the hell he was doing. (It's not unusual for those in Corbyn's position to find themselves sharing platforms with people whose wider views they find repulsive; not so common to big them up at great length after the fact.)

Corbyn fans' response to these unsettling revelations has been rather dismissive, even impatient. Again and again, the same responses: “Huh! Another smear!” Well no – a smear is something which isn't true. “Tony Blair met Hamas just last week – and no one had a problem with that!” Intelligent people, trying to pretend that they see no difference between a former Prime Minister and UN Middle East Peace Envoy – grotesquely amusing as that may be – attempting to negotiate a ceasefire in Palestine, and some obscure backbench MP, with close-to-zero power and influence, having a pow-wow with his curious “friends”. Whatever Corbynites claim, this is not international diplomacy. These were not summit meetings, nor were they peace talks; more like publicity stunts. Publicity stunts for peace, perhaps, or something similarly asinine and Lennonish, but still, the fact remains: there's no conceivable way that anything constructive – not one thing – could ever have come from any of them. And nor did it; only the provision of a platform for bastards.

Incidentally, wouldn't it have been nice to see, in amongst those shots of him sat next to Dyab Abou Jahjah – the Lebanese activist who rages against “Jew-worship” and describes gay men as “AIDS-spreading fagots” (sic) – pictures of Jeremy Corbyn hanging out with... I dunno, Bat Shalom, the joint Israeli-Arab women's peace organisation? Some of the many Israeli Leftists opposed to the occupation, but also to Hamas' thirst for genocide?

There is at least one Israeli citizen to whom Corbyn has chosen to extend the hand of friendship: Raed Salah, leader of the northern branch of the Islamic Movement in Israel, enthusiastic proponent of the “Jews did 9/11” theory and spreader of the Blood Libel. Now, there's really no point in talking to people like Raed Salah – other than to say “Fuck off, Raed Salah.” There's simply nothing to be gained. They have no interest in “finding common ground”... “a greater understanding”... “peace”. It's clear what Corbyn was thinking: Theresa May was trying to boot Salah out of the country at the time, on charges which Corbyn considered unfair. But the warmth with which he hailed his latest cause celebre was startling: “[Salah] is far from a dangerous man,” he gushed. “He's a very honoured citizen. He represents his people very well.” And, issuing an invitation to the House of Commons: “You will be assured of a very warm welcome, and I look forward to giving you tea on the terrace, because you deserve it.”

It just goes on and on: anyone who can be arsed to look will discover a list of crackpots, Jew-haters and general scumbuckets longer than both your arms. Corbyn seems to think that anti-imperialism is a simple thing: you just seek out some underdogs and slap them on the back. Never mind who or what they are; never mind the dungeons dark and gallows grim these “friends” provide for the secular Left, wherever they find them. Never mind if some of these “anti-imperialists” happen to subscribe to the most imperialist ideology that the world has ever seen. Never mind, never mind.

This stuff will undo him. It may well undo the Labour Party, too. This is not just “muckraking”. And this is not a trivial matter.

What's actually going to happen here?

The Labour Party is famously – or notoriously – reluctant to kick out its failed and failing leaders. If Burnham or Cooper should get this gig, only the fat hand of death would prevent them hanging on until at least spring 2020. If Corbyn wins, there are three possibilities: he could remain in place until the next election; he could be forced out, either by a coup from the Labour Right (who've never cared that much about internal party democracy), or by some public disgrace; or he could step down voluntarily in a couple of years on the perfectly reasonable grounds that he's ancient, and never really wanted the job.

The first of these scenarios could well lead to an electoral wipe-out. The second would spell the final defeat of the Left – and centre-left – within the party it created.

And so that third possibility is our best hope here, I think. But it assumes so very much. It assumes that Corbyn could nudge the Overton Window leftwards while in opposition (which is almost unprecedented), while under ceaseless, scurrilous – and sometimes well-founded – attack. It assumes that his successor would also come from the Left of the party, and would continue the good work which may or may not have been done while curbing the Corbyn-specific stupidity, cheering the party up, and then presenting as a credible PM. It assumes that three years of Corbynism would not have toxified the Labour brand to the point where it can only be handled with rubber gloves and tongs, from behind a sheet of reinforced plexiglass. It assumes that by this point, anyone will care what happens to the fucking poor, or whoever. How lucky do you feel?

Because this is a wager. With Cooper or Burnham there's a 50/50 chance we'll get our stake back, but we'll never get any more than that. With Corbyn, we could roll a double six and win the bank, but anything else and we've lost the watch, the car and the house; we're ruined. I'm not sure how lucky I feel. (A friend points out that the watch has stopped, the car is a write-off and the house has collapsed, so what have we got to lose? And I say, “Hmm.”)

One more thing: if Corbyn were to contend a General Election, it's worth considering who he'd be up against. Cameron insists he won't contest a third election, with George Osborne his anointed successor. That could be a gift to Labour – it's not just that Osborne is scum, it's that he can't conceal it. No one seems too bothered for now, so long as he's just some Igor lurching round Cameron's lab, but when that face has been on every TV screen in Britain for months, radiating smug malevolence, simultaneously spiteful and weak... that's not the customary front-benchers' mask, with its semi-convincing, stencilled-on sincerity. That's the face of a snivelling, evil bastard. It's unmistakable. Giving him that little Roman emperor's haircut hasn't changed a thing; Osborne may still be thought of as competent, but he will never be popular.

If on the other hand Boris Johnson finds a way to muscle in, all bets are off. Corbyn versus Osborne is at least a fight you can sort-of imagine the old man having. Corbyn versus Johnson goes like this:

Two days before Chelmsford, yet another row blows up. Someone's turned up footage of Corbyn, four years back, on Press TV – the propaganda channel of the Iranian government – describing the death of Osama bin Laden as “a tragedy”. Of course, that's not quite what he meant: if there's one thing surer than Corbyn's knack for saying unfortunate things, it's the media's determination to magnify and misrepresent them. Which allows the faithful to exonerate him, yet again – but despite these instant (and by now well-practiced) defensive manoeuvres, the truth is... well, the truth is bad enough.

Just as no one really thinks that Corbyn has a Hamas poster blu-tacked to his bedroom wall, no one believes he thought of Osama bin Laden as a superstud. We know what he meant: that an assassination, rather than an arrest and trial, appeared barbaric, and would provide more fuel for those who see Bin Laden as a martyr. Now, you could say that's a bit naïve – this stuff is shadowy, and we don't know the half of it, but it's unlikely that when those Navy SEALs burst in Osama threw his hands up and said “OK, it's a fair cop” – but it's a reasonable view. Barack Obama, too, says he'd have preferred to put Bin Laden on trial, for the same very obvious reasons.

But any politician with ambition should know better than to be so unbelievably careless. A tragedy? What was he thinking? Surely, if there's one essential quality required for the office of Prime Minister, or Leader of the Opposition – whether Right or Left – it's judgment. And if there's one thing Corbyn lacks, it's judgment. This is someone who still believes that Slobodan Milosevic was misunderstood; someone who signed an Early Day Motion calling for research into homeopathy to be “placed on the national agenda as a credible scientific field of inquiry”; someone who's already made it plain that he'd take Britain out of NATO if he could – even though he probably couldn't – thereby burning bridges which he hasn't even come to yet. (Deserting all our allies and then preaching them a sermon might cause certain folk to clap their hands in glee, but it's best avoided, really.)

It doesn't get any better, either: Corbyn went on to draw an equivalence between the death of the architect of 9/11, and 9/11 itself – oh yes he did – and anyway: what was he even doing on Press TV, best known for parroting the government line on Western journalists tortured for “spying”, and broadcasting theories of the Holocaust as perfidious Zionist hoax? It's not the only time he's popped up on there, never so ungracious as to criticise a government which hangs gay men from the gibbets of cranes – a government which he believes has been “demonised” by the West.

One or two of these clangers could be written off as “gaffes”; three or four you could brush under the rug... perhaps. But we seem to be looking at a lifetime of this stuff. And those of us who care about such things, and are prepared to say so, just face snarky, eye-rolling ridicule from people whose instincts are so acute that six years back they were telling us that George Galloway was a principled opponent of tyranny. (Corbyn, incidentally, sent a congratulatory tweet on the occasion of Galloway's victory in the Bradford West by-election. Always good for the party leader to be on record celebrating the election defeat of a Labour MP. Inspires loyalty, that.)

If you think these things don't matter – well, I suppose that's up to you. If you're going to hold your nose, the way you held your nose to vote for the party who brought us anti-immigration mugs and a pledge to be “tougher than the Tories” on social security – well, I can understand that. But please, don't be under any illusions. People keep comparing Corbyn to Michael Foot (and not in a nice way). But Labour lost in 1983 because its manifesto was simply too left-wing for the British electorate. If you're going to make yourself unelectable, that is at least an honourable way to do it.

This, I think, is not.

Anyway, look, why doesn't Corbyn have a campaign song? Everyone loves a campaign song. I suggest this one, by the ever-popular Ted Rogers. You have to change the words from "Dusty Bin” to “Jeremy Cor-byn”, but otherwise it fits quite well, I think.

So, Geordie comes back onstage and talks about blacklisting in the building trade, and then informs us that there'll be no Q&A at the end of the rally tonight because Jeremy's too tired. With that awesome, Howard Finkel-like introduction, Jeremy Corbyn takes the mic. They weren't kidding: he looks knackered, clinging to the lectern like a length of cobweb swaying in the breeze.

I've spent so long, these last few months, trawling back through Corbyn's recent past and finding demons that by now I'm half-expecting him to pull a piece of paper from his top-left pocket, read out the names of a third of the crowd, then have them dragged outside – by Roxy Jezel and the bloke with the man-bun – lined against the wall and shot. It's almost a surprise to get the man I voted for at two elections, that sincere and softly-spoken socialist, articulating my most deeply-held beliefs about the way we have to treat each other, while there is still time.

I'm no sourpuss; like everyone else in here, I applaud the things I agree with, and by the end of it my palms are sore. He talks about courage and strength, about the treatment of the mentally ill, about building social housing and controlling rents, establishing a baseline of decency. Low-key, small-scale, never trying to play the crowd. Treating them like adults, or equals.

What about the money, then? Once again he speaks in vague and reassuring terms about setting up a National Investment Bank – I'm broadly in favour, though partly because whenever he mentions it I get an earworm of the first Black Sabbath album – and everything is all so simple.

“So, we can raise corporation tax a bit...”

“A lot!” screams someone in the audience.

“OK, well...” he ad-libs weakly. “We'll take the bids later.”

This is not quite good enough. And I know it's not quite good enough, but... as he starts to wind up, it occurs to me I haven't really disagreed with anything he's said, and much of it has moved me almost to the point of real emotion. But, but, but, you see...

...that's the easy bit.

All he's done is offer up the very basic outline of a social democratic programme, and then waved his hands in place of explanations as to where he'd get the money – never mind what the holy hell he'd do about capital flight or uncontrolled inflation – but by God, these are filthy and desperate times, and if the things he said tonight were all he had to say, he'd have my vote tomorrow morning.

Finally, the crowd shriek their approval as he shrugs off the “abuse” he's been receiving from the media, as though it were all just tittle-tattle. We don't do that, he says. We don't deal with abuse. We don't respond to it. And for the first time tonight, I frown. And all around me, people are applauding, louder and louder.

On the way out, someone shakes a collection bucket under my nose. All I've got's a 50p and a 20p, and I'm not going to give him that.

“Sorry comrade,” I say. “I'm out of work at the moment.”

And he grunts and scowls.

Slumped on the train back to London, I suddenly remember that copy of Workers Hammer. I pull it from my bag and flip it open at a random page. It's an advert for back issues: some previous front covers, spread like a fan. One of them has the headline “HANDS OFF ROMAN POLANSKI! DOWN WITH AGE OF CONSENT LAWS!” (There is no comma halfway through the first of those injunctions.) I stuff it back in my bag with all the other crap and I stare through the window at the darkness instead.

We're speeding through an oblivious night, and London is approaching. Up in the newly-built towers a hundred thousand multi-coloured lights are sparkling, beaming; within sight, but out of reach. I think back to the clapping hands, and I have to remind myself: it's probably not going to be like that. It's going to be like this.

At Liverpool Street the tube is full of affluent-looking Londoners. We pull out of the station, and a homeless guy with half his teeth gone shuffles down the carriage waving a dirty paper cup. “Sorry to bother you, ladies and gentlemen,” he says, in a middle-class accent that's seen better days. “I'm trying to get the money for something to eat. I'm in a night shelter, and...”

I scrabble in my pocket and I give him what I've got – a 50p and a 20p – and shrug apologetically. He gets off at the next station. No one else has given him any money. I watched: they all made a point of staring straight ahead, unblinking, as he went by. Refusing to acknowledge his presence; refusing to acknowledge his existence.

Time is very, very short. The leaves have started falling already. The winter's coming on.