From the moment he became Labour leader, Jeremy Corbyn reminded me of someone, but I could never quite put my finger on who. Watching him at Glastonbury over the weekend, I suddenly realised. He is Coleridge's Ancient Mariner: the lugubrious, grey-bearded bore who, by some strange power, compels people to listen to his gloomy monologues.

I admire lots of things about Jezza. I like his honesty. I like his refusal to attribute base motives to people who disagree with him – something much rarer in politics than it should be. I like his personal decency and frugality. It's just that his view of Britain is that of an angry anti-colonialist student in the early 1970s.

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In Corbynland, everything wrong with the world is our fault. The IRA, Hamas, Hezbollah: all are creations of Western foreign policy. Jezza couldn't even bring himself to condemn Islamic State without a "but" about the American presence in Iraq. British nationalism is wicked, unlike Irish or Palestinian or Venezuelan nationalism. There is nothing to be proud of here: we are a mean-spirited, grasping people, who do not care about the poor. We are run by a gang of voracious bankers and their Tory puppets. Shame on us.

Now it is possible that, two weeks ago, two in five Brits suddenly decided to embrace this world-view, convinced that a spot of Venezuela-style socialism is just what we need. But my guess is that the majority of Labour supporters had other motives. First, and most obviously, Labour has a core vote: people who will always cast their ballots for that party, whether it is led by Tony Blair or Jeremy Corbyn.

Second, there were a number of groups who responded to the retail offers in Labour's manifesto: elderly people who don't want to pay for social care, public sector workers encouraged by the promise of a pay rise and, above all, students and their parents hoping for a remission of tuition fees.

Rather as happened during the recent American presidential election, the media never properly scrutinised the manifesto of the apparent joke candidate, instead concentrating on the serious one. So no one properly costed the impact of Corbyn's policies on economic growth. His assertion that all his goodies could be paid for by the rich and by reversing the recent cuts in corporation tax (which have actually seen revenue rise) was reported with a kind of knowing wink, as though readers could be trusted to see through it without needing it explained.

Sure, there is also a hard-Left nugget within that Labour coalition: a chunk of voters who want to requisition private property, abolish the Armed Forces, put businesses under workers' committees and so on. But it is far smaller than the two constituencies just mentioned.

Now here's the trouble for Labour. Corbyn and his Momentum supporters plainly regard the election result as a vindication of their brand of revolutionary socialism. The moderates in that party, including the vast majority of MPs, hung back when the manifesto was drawn up, letting Jezza own it so that he would own what they all assumed (as I did) would be a massive defeat on polling day. Other than on scrapping Trident and scrapping the monarchy, he pretty much got the programme he wanted.

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How have those Labour MPs reacted to his unexpected win? Have they stood by their principles, insisting that Labour is a party of the mainstream democratic Left rather than a Trotskyist movement? Have they reiterated their clear view that Corbyn's policies would bankrupt Britain? No. They have crawled back to him, simpering and fawning.

Which brings me back to the Ancient Mariner. You may remember from the poem that the Mariner committed the offence of shooting an albatross with his crossbow. At first, the other sailors turned on him, convinced that he had done a hellish thing: "Ah wretch! said they, the bird to slay, that made the breeze to blow!"

But shortly afterwards, there came a moment of false hope: a glorious sunrise.

Then all averred, I had killed the bird

That brought the fog and mist.

'Twas right, said they, such birds to slay,

That bring the fog and mist.

In endorsing the Ancient Mariner's crime, his crewmates made themselves his accomplices, condemning themselves to a terrible fate.

Is it not at least possible that the 2017 election was that false sunrise? That the British people, who have always eschewed political extremes, won't vote for a UK version of Fidel Castro or Hugo Chávez? That Corbyn's support will dwindle now he is finally being treated as a politician with a serious chance of office rather than as a sort of retro joke?

Perhaps I'm wrong. Perhaps the temper of this country has altered irrevocably, and our years of moderation are behind us. Perhaps we now regret the outcome of the Cold War. But just suppose, for a second, that I'm right. If so, then Labour can no longer treat Corbyn as an accidental leader. Every Labour MP who backs him is now implicated in his beliefs: the renationalisations, the borrowing, the anti-Americanism, the lot. Those MPs won't be able to shrug the whole thing off when Jezza is eventually toppled. Like the Ancient Mariner's crew, they have doomed themselves.

Daniel Hannan has been Conservative MEP for the South East of England since 1999, and is Secretary-General of the Alliance of European Conservatives and Reformists. Follow : @danieljhannan