On 25 March 2015, six months before becoming Labour leader, Jeremy Corbyn spoke in Westminster about “human rights and security in the Democratic Republic of Congo”. A long, U-shaped arrangement of chairs had been set up in the grand Commons committee room. “I am pleased that we are having this half-hour debate,” he began, in the flat, almost anti-rhetorical voice that had become a parliamentary fixture since his election 32 years earlier. Unshowily, he revealed that he had visited Congo twice, that he had “a considerable number” of Congolese immigrants in his constituency, and that he had a grasp of the country’s colonial and post-colonial history. “Sadly,” he said, “the horrors of Congo are not new.”

There was a sense, rare in Westminster, of politics being about life-or-death questions that extended across continents and centuries. But Corbyn’s entire audience consisted of a Conservative junior minister, a Democratic Unionist party MP, and four other people, two of whom chatted while he was speaking. Corbyn carried on, seemingly quite unfazed; in early 2015, as for much of his political life, promoting apparently lost causes before tiny audiences was what he did.

In the vast literature written about Labour between the 1980s and 2015 – all the fat gossipy memoirs, diaries and biographies, confident overviews by journalists and historians, and careful analyses by political scientists – there is an absence, which has seemed ever larger and more puzzling since Corbyn was overwhelmingly elected leader. He and his closest comrades for decades – John McDonnell, now shadow chancellor, and Diane Abbott, now shadow home secretary – rarely feature.

They are not in books about the 2003 Iraq war, which they all opposed. They are hardly in books about New Labour; or about the Conservative government and its austerity policies, which they opposed when their party barely did. They do not even feature much in studies of Labour’s startling success in London, where they all have constituencies and have hugely increased their majorities since the 90s.

Corbyn was elected to parliament in 1983, the same year as Tony Blair. From 1986 to 1993, Blair’s London home was in Corbyn’s constituency; and from 1993 to 1997, half a mile away. Many of the formative experiences of both politicians happened in the same small borough, Islington, long a favoured residence and subject for reporters. Yet for decades, most journalists, like most politicians, were preoccupied by the version of Labour politics pursued by Blair and his allies, which was slickly presented as the party’s only feasible strategy. Corbyn’s version – purist, sometimes crudely articulated – was assumed to be of little importance, and of minimal voter appeal.

In his decades on the margins, it was forgotten that he, Abbott and McDonnell had all been promising figures early in their careers. Corbyn had been the favoured protege of the socialist grandee Tony Benn. Between 1981 and 1985, McDonnell had been a key member of the radical and innovative Greater London Council. Abbott was the first black woman elected to parliament, in 1987. Yet by the end of that decade they all found themselves, as McDonnell put it in a 1998 documentary, “out in the wilderness”: leftwingers in a party and a country that seemed to be moving permanently rightwards.

Instead of careers, they had causes – anticapitalism, class struggle, peace activism, Irish Republicanism – towards which most other MPs were either increasingly apathetic or actively hostile. Westminster came to regard them with disdain. A former New Labour minister says that McDonnell was widely seen as “intolerant, hard, completely incorrigible”; Abbott as “very bright but fundamentally lazy”; and Corbyn as “naive” – “of no relevance” to the New Labour governments.

By 2015, the three comrades were all in their 60s. According to conventional wisdom, they had turned into a particular sort of British socialist: stubborn, unchanging, principled, passionate but often dour, uninterested in power, more influenced by the receding radical dreams of the 70s than the modern world. Supposedly more astute, ambitious figures had long written them off. In 1996, Blair discussed the state of the Labour party with the journalist Joe Murphy. “You really don’t have to worry,” said Blair, “about Jeremy Corbyn suddenly taking over.”

Since Corbyn first stood for leader, two popular interpretations of these wilderness years have emerged. One, favoured by the rightwing press and the Conservatives – and more quietly by some in the Labour party – is that he, Abbott and McDonnell spent these years as “loony left” fanatics and “apologists for terror”, as the Daily Mail put it in a long cautionary article the paper vainly published the day before this year’s election. This activism was a dead end, from which the three comrades escaped by fluke, thanks to the collapse of New Labour, Conservative divisions and mistakes, and foolish changes to the rules of Labour leadership contests.

The other interpretation, favoured by Corbynistas, especially older ones, is that these years of struggle were actually a long march towards the Labour left’s great breakthroughs in 2015 and 2017. “It laid the base for what’s happened since,” says Graham Bash, a leftwing activist and journalist who has been close to Corbyn since the 70s. A mainstream media fixated by parliament and dismissive of leftwing politics, this argument runs, did not notice that, on the streets outside, Corbyn and his comrades were steadily gaining credibility, converts and political networks.

The second interpretation may be too neat and coloured by hindsight – and too incurious about the illiberal characters with whom Corbyn and the others occasionally shared platforms – but it better reflects how the three comrades operated, and eventually came to power within the Labour party. On marches, at rallies, on picket lines, at occupations and at other events, however tiny or seemingly futile – at which other Labour MPs were rarely present – Corbyn and McDonnell were a familiar double act: McDonnell dapper and intense, Corbyn baggier in his dress and his sentences, both speaking with utter conviction, listening patiently to each other’s unvarying speeches, patting each other lightly on the shoulder afterwards. Abbott sometimes appeared with them. For decades the recipient of more racist and sexist abuse than probably any other MP, her public manner was more lawyerly and guarded; but she made exactly the same arguments.

Jeremy Corbyn MP being arrested in front of South Africa House in London in 1984. Photograph: Rob Scott

Abbott and Corbyn had been lovers as young activists in the late 70s. From 1987, they represented adjacent constituencies – Corbyn held Islington North, and Abbott held Hackney North and Stoke Newington – with intertwined leftwing subcultures. They remain close friends and allies today. McDonnell joined them in parliament in 1997, as MP for Hayes and Harlington in west London. Within a few years, Corbyn was publicly describing him as “my best friend in the House of Commons”. Their voting behaviour was almost identical: during Blair’s first government – according to Philip Cowley, the authority on Commons rebellions – Corbyn defied the Labour whip 64 times, and McDonnell did 59 times, almost always on the same issues. They were the two least-obedient Labour MPs, and remained so after their party lost power in 2010. Abbott was also consistently high on the list of Labour dissidents. By 2015, they had been MPs for 78 years between them, and had held no ministerial positions.

Rarely in Britain has such a marginal, ideological group become so dominant in a party, so influential in how other parties and the country discuss fundamental issues, and so electorally powerful. The last time such a takeover happened was with the Thatcherites in the 70s. But Thatcher and her band of Tory rebels were, relatively, establishment figures: ex-ministers who had been out of power only a few years, backed by national newspapers, influential thinktanks, and parts of big business.

The ongoing argument about Corbyn and his comrades’ much lonelier, much longer and more formative wilderness years is really an argument about the validity of Corbynism’s political methods and ideas. It is also an argument about the long-term direction of British politics, ever since Thatcherism became dominant in the mid-80s.

Corbyn, Abbott and McDonnell’s activities between then and 2015 challenged deep assumptions, still widely held today: about the superiority of capitalism over socialism as a political cause, and about Labour’s need to adapt itself accordingly; about Westminster and the mainstream media being the only political arenas that matter; about political change needing to come quickly from the top, rather than slowly from the bottom; and about what constitutes a useful political career.

What important things about Corbyn, Abbott and McDonnell did most people miss between the 80s and 2015? And beyond the hostile caricatures and heroic myths, what did the three comrades actually do during these years? The period was not as monochrome and unvarying for them as their detractors often insist: it featured advances and retreats, alliances and splits, quiet compromises as well as outspoken defiance. Contrary to the caricaturists, the three comrades did not just teleport from 1980 to 2015. The period changed them. And their political lives during these hard years give us hints about how, if Theresa May’s ever-wobblier administration topples, they might approach an even harder task than surviving on the margins: running a truly leftwing British government.

The 80s are usually seen as the right’s decade. But at the start of it the Labour left felt it was close to taking power. The Thatcher government was new and deeply unpopular. The Labour right seemed discredited, after the recent failures of Jim Callaghan’s pragmatic government.

The left’s hopes were particularly high in London. In then-scruffy boroughs such as Hackney and Islington, immigrants and middle-class incomers with leftwing views were replacing traditional Labour voters, just as they are now. Corbyn and McDonnell both moved to the capital as young activists in the 70s: Corbyn from a family of middle-class socialists in Shropshire, McDonnell from a working-class trade union background in Liverpool and Great Yarmouth. Before committing to politics, McDonnell had tried training as a Catholic priest. Abbott, born in London to Labour-voting parents from Jamaica, was also drawn during the 70s into this leftwing ferment.

In 1980, a fierce newsletter called London Labour Briefing began appearing. Chris Knight helped found it. A veteran of far-left politics, he had decided that Labour, rather than small sects, offered the best opportunity to change Britain. “I realised that Labour is colourless,” he told me. “The colour of the party depends on which faction has the most influence.” The strategy the newsletter wanted Labour to adopt, he said, was democratic but aggressive: “Get a majority. Enact your legislation. Then dismantle the establishment when it challenges what you’re doing.” The newsletter’s slogan was adapted from one of Lenin’s: “Labour – Take The Power!”

Briefing, as it became known, had a circulation of a few thousand. But it was punchily written, and as well as radicalising the London Labour party, it addressed racial and sexual equality – concerns that were beginning to create a more cosmopolitan socialism, the antecedent of Britain’s leftwing culture now. Corbyn fitted easily into the Briefing world. “Jeremy would pop in, have a coffee, write an article,” Knight remembered. In March 1982, Corbyn attacked “the lunatic Right” of the Labour party. He also wrote that Labour councillors should never collaborate with Conservative counterparts, but “look outwards to the working class” for support against Thatcher’s austerity policies. When Corbyn was elected to parliament in 1983, Knight and the Briefing collective saw a breakthrough: “It was extremely important for us to have an MP. Jeremy was the first.”

“The Commons is a great base to be a revolutionary from,” says Hilary Armstrong, a much more orthodox Labour MP who served from 1987 until 2010. “You hear what’s going on. You have status in the outside world.”

But Briefing had already achieved a seemingly bigger advance. In 1981, one of its co-founders, Ken Livingstone, became leader of the Greater London Council (GLC), then the capital’s prestigious municipal government, after mounting an internal coup against the Labour right. Briefing’s front page rejoiced: “London’s Ours!” That same week, as Livingstone told me recently, “François Mitterrand was elected president of France on a socialist platform. We were all thinking: ‘The world’s about to change.’”

From left: GLC members Ken Livingstone, John McDonnell, Ken Little and Lewis Herbert in 1984. Photograph: PA Archive

Livingstone made McDonnell his deputy. Barely 30, McDonnell was already an experienced union official with a reputation for mastering paperwork – he still proudly describes himself as “a bureaucrat” – and for relentless, dogmatic politics. “John had more of that revolutionary edge than Jeremy,” Bash, who worked at Briefing, told me. “Jeremy would work with revolutionaries, but he was never one himself.”

McDonnell became the GLC’s deputy leader and chair of finance, a role he has described since as “London’s chancellor”. In reality, the GLC had limited revenues, and the Thatcher government worked hard to limit them further. But McDonnell became adept at finding unforeseen sources of funds, and then distributing them in radical new ways. To the fury of the government and its press allies, tax income raised by the GLC from businesses became grants for feminist groups and nuclear disarmament. The GLC revelled in its underdog victories. In a 1984 staff pantomime, Livingstone played Dick Whittington, and McDonnell his cunning cat.

In 1985, Diane Abbott became a GLC press officer. More openly than Corbyn or McDonnell, she had long been “interested in power”, as she put it to me: for herself, and for egalitarian goals. She had pursued it as a pioneering black working-class student at Cambridge, and through brief jobs at the Home Office, in television, and at the National Council for Civil Liberties (now Liberty). She was also involved in a campaign to persuade Labour to create “black sections” for non-white members. And she wanted to become an MP.

The safe seat of Hackney North already had a well-liked MP from the Labour left, Ernie Roberts. But he was white, the constituency was increasingly multiracial, and there were no black MPs at all in the Commons. For months, Briefing and the party’s black sections activists, with support from Corbyn, worked to persuade the Hackney North party to replace Roberts with Abbott. “It was a tough decision,” said Bash, who was a member of the Hackney party. “Diane was a bit to the right of Ernie. But she was a black woman, and she was sufficiently on the left to warrant support.” At the decisive meeting, she made a stirring socialist speech, delivered with crisp Cambridge diction, and squeaked home by seven votes.

Even as the candidate, Abbott remained a slightly isolated, underestimated figure. Almost three-quarters of local voters were white, she was regarded (inaccurately) by the Labour right as a dogmatic black separatist, and the Conservative candidate was a charming young man called Oliver Letwin. During the 1987 general election, the glass front of Abbott’s campaign office was smashed in, and the Conservative party chairman, Norman Tebbit, insinuated that an arson attack on Letwin’s own office might have been Labour’s doing.

Yet Abbott won easily. “I have come a long way,” she said at the election count, with a huge smile. “I am aware that a lot of hopes, not just in Hackney, but across the country, ride on our victory tonight.” The room was jammed with jubilant black and white activists of all ages. Abbott and three other Labour candidates had become the first non-white MPs since the 1920s. On her first day in the Commons chamber, Abbott took the seat previously occupied by Enoch Powell.

But radicals often kid themselves that their moment has come. During the mid-80s, away from inner London, the power of the left was evaporating. The Conservatives won election landslides in 1983 and 1987. In 1985, they beat the miners’ strike, which many on the left had hoped would bring the government down. In 1986, Thatcher abolished the GLC.

At Briefing, the atmosphere changed. “After the miners were defeated, I thought: ‘It’s going to be quite a few years before our turn comes again,’” Knight remembered. The Labour left did not rethink its ideas, but it lost confidence. In the late 80s, Briefing dropped its slogan “Take the Power!” Over the next dozen years, the veteran activist and Corbyn ally Tariq Ali told me, “Lots of people in far left groups effectively gave up, or went over to the other side.” The Communist party journal Marxism Today began running awestruck analyses about the modernity of Thatcherism. The Welsh ex-leftist Neil Kinnock became Labour leader in 1983, and quickly turned against the metropolitan socialists his predecessor, Michael Foot, had tolerated. “The heart of the party was now outside London,” says Chris Smith, who, like Corbyn, became an Islington MP in 1983. “London MPs had constantly to prove to the leadership that we weren’t loonies.”

Jeremy Corbyn in 1984. Photograph: Peter Brooker/Rex/Shutterstock

Not that Corbyn tried very hard. In parliament, while civil to his superiors, he continued to dress like a 70s activist: long hair and beard, earth-toned jumpers, rarely a tie. He made short, plain speeches that were either slightly shrill, bulging-eyed condemnations of Kinnock’s compromises, or hazy statements of faith in socialism’s prospects. In 1988, Corbyn helped Tony Benn stand against Kinnock for the leadership. Benn lost by 89% to 11%. Corbyn was asked by a BBC Newsnight reporter whether the contest had been “a euthanasia of the left”. “Not at all,” said Corbyn, expressing a faith in street politics that was long regarded as delusional until his leadership and general election campaigns. “We had a rally here last night of over 500 people … It’s the rebirth of a serious, thinking left that’s looking forward, beyond the 80s.”

Abbott also seemed out of step with the times. The Labour leadership, the Conservatives, and the press all treated her election as a sinister advance by what they pejoratively called “the hard left”, rather than a long-overdue victory for diversity. In fact, despite her smooth public persona, she initially found the expectations and rituals of Commons life quite paralysing: “I was in a kind of daze,” she said later. A former Labour activist who has known her for decades told me Abbott felt lonely as a young MP: “She used to ring me up all the time. She was quite needy.”

For McDonnell, the shift from prodigy to outcast was even starker. In 1985, he lost his GLC positions after a row with Livingstone. They had been part of an optimistic scheme by leftwing councils to protect their services and to destabilise, or perhaps even topple, the Thatcher government by illegally refusing to set budgets, while the government was busy with the miners’ strike. But when the strike collapsed, and councils outside London began to back down, Livingstone wanted to abandon the no-budget strategy. McDonnell did not. With a fury that was only partly calculated, he took this internal dispute to the media. “Ken is a friend,” he told the London radio station LBC, “but there is no doubt that he has betrayed the whole campaign in order to save his political career.”

McDonnell’s stance was supported by many on the left. But the more senior, more realistic Livingstone got his way. From 1985 until 1997, McDonnell almost completely disappeared from the national press. After the GLC, he took less controversial, more technical roles for London boroughs. He stood as an MP for Hayes and Harlington in 1992, but lost by 53 votes, and was forced to pay damages for libelling his equally abrasive Tory opponent, Terry Dicks. “I was out in exile, basically,” McDonnell said later. “Personally, it was distressing.”

By the mid-90s, McDonnell, Abbott and Corbyn were all in their mid-40s. Their years of youthful promise were gone. And the next shift in the political weather, from the Conservatives to Labour, would only push them further to the margins.

Frustrated exiles need coping strategies. For his first nine years in parliament, Corbyn shared an office with Bob Clay, the leftwing Labour MP for Sunderland North. Increasingly as the years passed, Clay told me, “We didn’t discuss the state of the party. Jeremy’s view was: ‘This is all very difficult. I just want to get on with things, Bob.’”

“Things” often meant foreign causes. More focused MPs soon came to feel that Corbyn’s preoccupations were infinite in number and scale. “Whenever you saw him, he always had a large pile of documents,” says a former Labour MP who was also a campaigner against injustices. “He’d be arriving late, or departing early for the next meeting.” The former MP says Corbyn made too many political gestures: “Many of his causes were things you couldn’t do anything about.”

Clay disagrees. “During the civil war in Colombia in the 90s, when the thugs picked up a trade union leader, they’d usually be dead in 48 hours. Jeremy would get a fax saying, so-and-so’s been lifted. There would be no interest from the [Labour] front bench. He and I would get as many MPs as possible to sign a letter of protest to the Colombian embassy. Very often, it did the trick.”

Corbyn also did practical politics in his constituency. Less prestigious than Blair’s Georgian Islington to the south, Islington North is a tight knot of council estates and comfortable houses, polyglot cafes and thundering roads, one of the most crowded and diverse seats in the country. Corbyn quickly made himself ubiquitous. “It’s almost like a drug for him,” says Keith Veness, a close friend who was his constituency agent during the 90s. “He knocks on a door, and some guy from Paraguay starts telling him about all the issues. And then you can’t get Jeremy out of there.” Last year, Corbyn told Vice News, “Every single person you meet knows something you don’t.”

In 1983 the constituency party bought a building on the busy Seven Sisters Road as a base for this street politics. The Red Rose, as it became known, was a former cooperative hall with a tiny caretaker’s flat above, which became his office. “For Jeremy’s surgeries,” says Veness, “you’d have 100 people waiting, on a Friday night, sitting on the stairs, out in the street.” To raise funds, the Red Rose had a raucous bar, and a club that hosted alternative comedy, feminist workshops and speeches by union leaders. “Jeremy had no problem pushing through a group of drunks to get up to the office,” says Veness. “He thought it was all marvellous, because he was a man of the people.”

Diane Abbott, the newly elected Labour MP for Hackney North, at the opening of parliament in 1987, with fellow Labour MPs Bernie Grant (top), Jeremy Corbyn (right) and Tony Banks (bottom). Photograph: PA

The Red Rose increasingly became Corbyn’s refuge. “He’d spend all day there, and go to the Commons in the evening,” Veness says. “He had a beaten-up old car, and used to claim he could get to the Commons in eight minutes.”

Corbyn had developed a politics that worked, up to a point, without Westminster. Abbott found it harder. In Hackney, the tensions and expectations surrounding her selection as a candidate and subsequent election lingered. She was threatened by racists, and by black separatists who believed she should not work with white MPs. She did not move through the unevenly gentrified streets of her constituency as constantly and confidently as Corbyn did, but lived at first in a gated road.

In parliament, unlike him, she could be dazzling. In 1990, when Michael Heseltine began to hint that he would challenge for the Tory leadership, Abbott taunted Margaret Thatcher - who still regularly crushed Labour MPs in debates – that “the best she could hope for in a Heseltine administration” would be “mayor of Dulwich”, the London suburb where Thatcher had bought a house for life after Downing Street.

Less helpfully for her prospects, Abbott also showed no deference towards Labour leaders. In 1996, backbenchers were summoned in groups to see Blair, then the lauded premier-in-waiting. The former Labour minister Chris Mullin records in his diaries that Abbott “waltzed in 20 minutes late”, then told Blair that New Labour made people feel “talked at rather than listened to”, and was “losing sight of those who traditionally voted for us”.

These would turn out to be acute criticisms. New Labour would increasingly take leftwing and working-class voters for granted, assuming they had no other party to vote for, and would shed millions of votes as a consequence. But in the 90s, this process had barely begun. In 1997, the party returned to power with its biggest-ever majority. Abbott’s attacks on Blairism, which were echoed by Corbyn, sometimes sounded more like outdated dogma than shrewd warnings.

The first half dozen years of the Blair government were a tough new environment for Labour dissidents. As Lewis Minkin shows in his 2014 book The Blair Supremacy: A Study in the Politics of Party Management, New Labour’s control-freak reputation concealed a subtler, more effective approach to rebels.

The Labour left’s parliamentary vehicle, the Socialist Campaign Group, had been set up in the early 80s. By the late 90s, it was still meeting weekly, assessing government policy, and organizing Commons revolts. But it only had about 30 members, including Abbott, Corbyn and McDonnell, and most of them were middle-aged or older. Frequently, members died, or moved rightwards, or, like Bob Clay, Corbyn’s former officemate, left politics altogether. Since Labour had a majority of more than 160 between 1997 and 2005, the more patient Blairites realised there was no need to silence the group, or expel its most disloyal members from the party. Blair worried that doing the latter would remind voters of Labour’s splits during the 80s.

Instead, new MPs were discouraged from joining the group – or even contacting its members. The former Labour MP and group member Alan Simpson recalls: “The whips would say: ‘You want to be careful having conversations with Jeremy Corbyn. Careers can be ruined that way.’”

So, for much of the Blair government, Corbyn and Abbott’s Westminster lives were in a kind of limbo. They were not controlled – Corbyn was not given a pager, New Labour’s electronic prod for herding MPs – but they were not influential. They were kept off Commons select committees by the party hierarchy. They had little dialogue with the Blairites. “Jeremy Corbyn would never engage in an argument with you,” says Hilary Armstrong, Blair’s chief whip from 2001 to 2006. “His head would go down. He’d look at the floor.”

Diane Abbott in 1986. Photograph: PA

Even some of Abbott and Corbyn’s constituents (I’ve been one since 1994) voted for them as moral symbols rather than figures with any Commons clout. According to Minkin, Blair’s strategist Peter Mandelson had a phrase for what he wanted the parliamentary left to become: “a sealed tomb”.

Over-confident about the prospects for capitalism and centrist politics, the Blairites did not foresee that if economic circumstances changed, the left might clamber out.

One warning sign came as early as the 1997 election. McDonnell took Hayes and Harlington with one of the largest swings to Labour in the country. Hayes was different from the left’s previous London strongholds: an outer suburb, with smartened-up semis and flash cars in driveways, small businessmen rather than middle-class bohemians, but also a history of deindustrialisation and low wages. It was the sort of place where Labour often struggled. But McDonnell won it through typical relentlessness. He had lived there since arriving in London more than 20 years earlier. During the 70s he had been an activist for local tenants’ organisations and law centres. During the 80s, he had been the area’s GLC councillor. During the 90s, he had supported campaigners against the growth of Heathrow airport, which dominated the constituency.

“The work John did in Hayes was like what Jeremy had done in Islington: involving party members, constantly campaigning,” Veness told me. His wife, Valerie, who used to work as Corbyn’s personal assistant, remembered: “I went to Hayes with Jeremy lots of times. John’s meetings were always packed tight: white working class, lots of Sikhs. They all loved John. People in the local party who didn’t share his politics still loved him.”

McDonnell’s constituency office was, and still is, almost comically no-frills: a large pebbledashed hut, the door paint ripped by years of taped-up notices. Since the early 2000s, one regular visitor has been John Stewart, an opponent of Heathrow expansion who has known McDonnell since the GLC. “John has always been comfortable dealing with people who aren’t in the Labour party,” says Stewart. “John is blunt. He doesn’t suffer fools. But because he is so sure about his own ideological position, it gives him a bit more freedom, in his own mind, to work with others. And he is able to outline a campaign strategy in terms ordinary people understand. For years, more mainstream people I met through Heathrow – Labour people, Westminster lobbyists – would say to me: ‘John McDonnell is a wasted resource. If only he would modify his politics.’”

In 2009, when Gordon Brown’s government approved a third Heathrow runway without a parliamentary vote, McDonnell made a Commons speech that switched with characteristic speed from studied calm to finger-jabbing fury; then he grabbed the chamber’s ceremonial mace, and was suspended from parliament. MPs and Commons observers saw it as a sign of dangerous immaturity. But others saw his anger differently: “Young green activists, suspicious of traditional politics, made an exception for John,” says Stewart. Unlike most MPs, McDonnell supported non-violent direct action. Like Corbyn, he often seemed more the protesters’ representative in the Labour party than the other way round.

During the 00s, Abbott also raised her profile. Less patient, less concerned with ideological consistency, and a single mother – she was widely criticised on the left for sending her son to private school – she could not and would not turn herself into a permanent campaigner. Instead she became the left’s representative on television. From 2004 to 2010, she was a commentator on the cult BBC2 show This Week. The late-night programme had an unbuttoned, only loosely party-political feel. Abbott’s distance from New Labour’s increasingly worn-out orthodoxies, her pithiness, and her preference for thinking out loud rather than sticking to prepared briefs, made her more watchable than her many enemies expected. She flirted on the short studio sofa with her fellow commentator Michael Portillo, himself once a rising star of the Conservative right. “You couldn’t watch her and think,” says the show’s executive producer Samir Shah, “‘Here’s a dogmatic, hard-left figure.’”

She began appearing on other programmes, often competitive ones: University Challenge, Pointless, Come Dine With Me. For the latter, in 2011, she hosted a boozy supper in her house in Hackney. Then the show briefly showed her at her Westminster office. The desk and shelves were heavy with box files, spines clearly legible: “Gun Crime”, “Guantanamo”, “Black Nurses Project”, “Black Socialist Society”. It felt like clever political product placement, but also poignant, and exasperating: as if a radical talent was being frittered away.

Corbyn, like McDonnell, made his plainer political gifts go further. In 2001, he helped found the Stop the War coalition. It brought together many of his causes, and showed that he was not necessarily a political loner. In February 2003, his fellow Islington MP Chris Smith – much less leftwing, and a former New Labour cabinet minister – helped table a Commons amendment that the case for war against Iraq was “as yet unproven”. Smith recalls: “It wasn’t as strongly worded as Jeremy would have wanted. It had been drafted to appeal to as diffuse a group as possible, in order to maximise support. But Jeremy was prepared to get three-quarters of a loaf.” He was finally becoming a slightly more flexible Westminster politician.

The amendment was supported by 121 Labour MPs – the biggest backbench revolt since 1846. The same month, Stop the War mobilised a million people, many of them not leftwingers, to march in London. Blairism’s claim to be a unifying national force, for almost a decade the most potent weapon in British politics, had begun to break down, and New Labour would never fully recover.

But in the conservative world of British politics, decaying orthodoxies can live on for a long time. From the Iraq war until 2015, the Labour left groped for ways to supersede New Labour. What press interest there was in Labour dissidents focused on less ideological but better-known figures than Corbyn: Robin Cook, Clare Short, and Ken Livingstone, now mayor of London. In 2006, Corbyn told the Guardian he was considering standing for the Labour deputy leadership as “an anti-war candidate”. But he changed his mind, not fancying the attention or his chances.

Instead, when Blair finally stepped down in 2007, McDonnell ran against Brown for leader. McDonnell published his manifesto as a short book, Another World Is Possible. It had a small red star on the cover, like a bashful echo of a Soviet pamphlet. The book was full of ambitious ideas: a universal basic income, a land tax, renationalised industries run democratically rather than by “remote state bodies”. It showed McDonnell thinking harder and less dogmatically about the economy – which was beginning to lose momentum after the extended Blair boom – than the New Labour figures who still regarded him as a Marxist throwback. Some of the ideas were ahead of their time: they would appear in Labour’s much-praised 2017 general election manifesto.

But at the leadership hustings in 2007, McDonnell seemed nervous. He was over-deferential towards Brown, barely mentioned any of his alternative policies, and never suggested he had any chance of becoming leader. Candidates needed nominations from 45 MPs to fight the contest to the end. He got 29.

A few months later, the financial crisis began, and with it the vindication of some of McDonnell’s anticapitalist arguments. But when he ran for the leadership again in 2010, he could only gather 16 nominations. One reason was his lingering Commons unpopularity. The other was that Abbott was standing as well.

The bureaucrat and the improviser had never quite trusted each other. He saw her as indiscreet and erratic. She saw him as scheming. At the Mile End Institute in London this March, she said of her shadow cabinet colleague: “John McDonnell has done his best to transform himself into a friendly, bank manager-type figure, which, if you know John McDonnell as well as I do, is … interesting.” She and the audience laughed knowingly.

McDonnell in 2006, announcing his intention to stand for the Labour leadership after Tony Blair’s departure. Photograph: Alastair Grant/AP

Unlike him, she secured enough nominations to stay in the race, by persuading MPs outside the left that she would lend variety to a contest dominated by white men. Abbott came fourth in the final vote, but Corbyn’s biographer Rosa Prince argues that a crucial precedent was set. When he ran for leader in 2015, his campaign coordinator, McDonnell, cited Abbott’s 2010 candidacy to argue that “all wings of the party” ought again to be “represented”. So confident were MPs on Labour’s right that Corbyn had no chance, enough of them agreed to support him.

The Labour left is so caricatured by its opponents that they often misread its true strength. In the early 80s, the ability of Abbott, Corbyn, McDonnell and their comrades to challenge Thatcherism was hugely overestimated. They were too young and inexperienced, too lacking in support outside inner London, and too many social trends were running against them, in favour of individualism and the free market. In 2015, after the financial crisis and the ineffectual grind of austerity, the prospects for free-market politics were almost the exact opposite; but the Labour left’s ability to outflank Thatcherism and its descendants was hugely underestimated. Most politicians and journalists still believed that only a limited amount could be achieved in British politics, especially by the left.

That caution may finally be going now. At this year’s Labour conference, amid crowds of excited millennials, Corbyn and McDonnell seemed to revel, a little prematurely perhaps, in their success and shared history. They wore identical outfits – black suit, white shirt, red tie – that combined would-be ministerial sobriety with a hint of the old revolutionary. During McDonnell’s speech, Corbyn, sitting on stage to his left, unself-consciously produced a phone and took a picture of the political intellect he most admires. During his own speech, Corbyn praised Abbott for her “decades-long record of campaigning for social justice”, then announced it was her birthday. As a full minute’s applause followed, Abbott, who was at the front of the hall, looked simultaneously surprised, delighted and a little unsettled. Being appreciated by the party seemed novel.

All over Brighton, there were delegates in their 50s and 60s, wearing denim jackets covered in socialist badges, exactly as they might have during the left’s expectant days in the early 80s. “They’ve all come back, the people who drifted away from the struggle,” Valerie Veness told me contentedly. But then her tone hardened: “People like Jeremy and me – we were a slightly tougher group. We didn’t give up.”

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• This article was amended on 6 and 14 November 2017. An earlier version omitted Tony Banks’s name in a photo caption. In addition, an earlier version referred to Keith Veness as Jeremy Corbyn’s constituency agent during the 80s and 90s. Richard Hadley was Corbyn’s agent during the 80s; Veness was his agent during the 90s. This has been corrected.