Hours after being announced as the new leader of the British Labour Party, Jeremy Corbyn was addressing tens of thousands of demonstrators at a rally in support of refugees in London’s Parliament Square. Behind the stage, as his speech drew to a close, a phalanx of young volunteers in bright red “TEAM CORBYN” T-shirts arranged themselves into a protective cordon ready to speed their leader through the throng of ecstatic supporters, TV cameras, journalists and selfie-seekers waiting for him.

Just three months earlier, after another large rally in June, Corbyn had lingered in exactly the same spot, undisturbed, chatting freely with passing well-wishers. It is impossible to overstate how unlikely it seemed then that Corbyn, a veteran rebel MP from the left wing of his party, would soon be leading Her Majesty’s official opposition. For decades marginalised by his parliamentary colleagues and ignored by the media, he is the ultimate outsider, swept to victory by a grass-roots phenomenon that elected him with 59.50f the vote, a whole 40 points clear of his nearest rival on 19It is a mandate unparalleled in British political history.

In fact the June rally, at which Corbyn spoke, gave the first sign that something extraordinary might be about to happen. Called in an atmosphere of despondency on the left after the Conservative Party’s general election win in May, the anti-austerity protest unexpectedly attracted hundreds of thousands of demonstrators — and potential Corbyn voters. “There was a movement looking for a home,” says the comedian Mark Steel, one of the founders of the People’s Assembly, the broad umbrella organisation for campaigners and unions, which organised the protest. “No one quite spotted that it would come out this way, but here it is.”

That this movement took the form of a Jeremy Corbyn leadership campaign is doubly surprising because the man himself is the antithesis of the stereotypical leftwing firebrand. Without the rousing oratorical skills of his mentor, the late Tony Benn, and with none of the raw charisma of Alexis Tsipras, Corbyn was not perceived as a threat by his fellow MPs. Remarkably, Corbyn’s straightforward, unspun style became an asset, marking him out as a total contrast from the media-trained salesmen of the British political class.

Electrical charge already in the air

Rather than being the conjurer of a movement, Corbyn acted as a lightning rod to conduct an electrical charge already in the air. His support is mixed in age and background, but there are at least three discernable categories. The first and most prominent group is the young, for whom post-2008 neoliberalism has meant poor job prospects and extortionate rents. It is no coincidence that the archetypal Corbyn supporter is fresh-faced, highly educated and probably works in a coffee shop. This age group was politicised by the tripling of university tuition fees in 2012, which created a generational grudge and a much more radical student movement than Britain is used to.

A second pillar of support is the anti-war movement. Corbyn was until recently chair of the Stop the War Coalition, which organised the two-million-strong march against the invasion of Iraq in 2003 — the biggest protest in British history. Lindsey German, Stop the War’s convener, believes the legacy of that demonstration “very much fed into” Corbyn’s campaign. “That was a huge number of people who hated what Labour did, who resented Tony Blair,” she says. “A lot of older people who left Labour over Iraq will now go back.”

The importance of street protests is reflexively dismissed by the British media, but no account of the Corbyn phenomenon is complete without them. Corbyn has addressed so many demonstrations on such a range of causes — from Palestine to mental health — that he could count on a core of motivated supporters from the moment his candidacy was announced.

The third group is the organised working class. On the face of it, this is hardly surprising. In the public sector, where trade unions still have strength, pay has been frozen for years and services cut and privatised. Many unions are now led by left-leaning general secretaries. Even so, it was a shock to the Labour establishment when the biggest unions, Unite and Unison, endorsed Corbyn in response to grass-roots pressure.

Many of these drivers are familiar across Europe. What is different about the UK is that there is no tradition of successful parties to the left of Labour. The first-past-the-post voting system ensures that smaller parties like the Greens are all but locked out of parliament. With no possibility of electoral success for a British Syriza or Podemos, the anti-austerity sentiment has instead found expression in the Labour Party itself, which many had thought irreversibly Blairised.

Corbynmania takes hold

Labour was transformed by a membership surge and a new system for electing its leader. Anyone could vote if they paid a one-time fee of £3. The scheme originated from the right of the party: Blairites, besotted by American primaries, thought that opening internal elections to the general public would diminish the influence of union members and anchor Labour in the fabled centre ground. To their horror, the £3 offer was taken up by the left, who appreciated the irony of using a Blairite mechanism against the Blairites. The format was perfect for social media — allowing people to sign up with a click and encourage their friends to do likewise — which was a great advantage to Corbyn, who has strong support on Facebook and Twitter.

“We’re talking about a dynamic that happened outside the Labour Party, and then because of the change of structure it was echoed inside,” says Hilary Wainwright, a socialist feminist author and long-time political collaborator with Corbyn. She says the buzz around Corbyn’s campaign “gave existing members the confidence to vote for him, and helped create the sense of a mass movement with big meetings.” Corbyn addressed 99 gatherings around the country, often having to make extra speeches in the street outside for those unable to fit in. People called it Corbynmania.

The question for the future is whether this mobilised constituency will be strong enough to shield Corbyn from the attacks coming his way, and indeed whether it can be sustained. An onslaught is inevitable because on many issues Corbyn’s positions are directly opposed to what the British state considers to be its interests. He finds it difficult to think of circumstances in which he would deploy British military force, opposes bombing Syria, would not renew Britain’s nuclear weapons, and is critical of NATO’s “global role”. On the economy, he would confront the financial industry in the City, exert political control over the central bank, and overturn Thatcherite orthodoxy by renationalising railways and utilities. He is ambiguous on Brexit (UK exit from the EU), arguing for a reformed “social Europe”. He is a fierce critic of Europe’s treatment of Greece, and of the planned TTIP trade deal between the EU and the US.

How many of these positions will become official Labour policy is not yet clear. Between the leader and the membership — who are broadly aligned — stand Corbyn’s fellow Labour MPs, his biggest obstacle. Most were selected during the Blair-Brown era and have spent their careers defining themselves against the left. “No one has ever tried to lead the party with such little support among the MPs,” says Lance Price, Tony Blair’s former director of communications. “Jeremy Corbyn is going to have a very difficult job.”

Corbyn’s strategy is to democratise the party, restoring decision-making powers to the annual conference to circumvent MPs’ opposition. Price believes Corbyn has “an awful lot of the levers of power in his hands,” and regards the idea of “a far-left leader trapped in a party where the policy platform is somewhere different” as unlikely.

Split or self-destruct?

Some MPs are already talking darkly — but anonymously — of a split, but the prospects for such a move do not look good. The Blairites have been humiliated in the leadership contest. Their candidate, Liz Kendall, received just 4.50f the vote. Their problem is ideological. Whatever dynamism Blairism had, it sprang from sources not available in the post-crash economy.

It is more likely that the right will seek vengeance within the party, even if this proves self-destructive for Labour. Corbyn’s opponents can easily muster the 47 MPs needed to trigger a new leadership contest. The size of Corbyn’s victory precludes a move in the short term — an infuriated membership would simply elect him again. The right will wait for an opportune moment, such as after local, Scottish or European elections, if Labour does badly in them. In the meantime they will brief against Corbyn in the press and block his policies in parliament.

Ken Livingstone, the former mayor of London and a Corbyn ally, has a less doom-laden outlook, saying Labour MPs “don’t really matter because if Jeremy can connect with the British public, and the polls show he’s going to be the next prime minister, all these MPs are going to be sucking up to him in the hope of getting a job.”

Compared to Corbyn’s own colleagues, the Conservatives seem more straightforward opponents. Their strategy is crystal clear, demonstrated in an attack video painting Corbyn as sympathetic to Hamas, Hizbullah and even Osama bin Laden. Their aggressive approach was encapsulated in a tweet from David Cameron that read: “The Labour Party is now a threat to our national security, our economic security and your family’s security” (1).

“What signal does that send to MI5, to the security services?” asks WikiLeaks founder Julian Assange, a man with extensive experience of intelligence agencies. Assange, whose plight Corbyn has raised in parliament in the past, believes that if the Labour leader maintains a strong line on Trident nuclear weapons and NATO, “that would release significant resources devoted to stopping him before an election. If he looks like becoming prime minister the stakes are so high that a lot of things are possible.” Assange believes Corbyn should take this threat seriously. “He has already pulled back from saying he would withdraw from NATO. It is wise not to fight on all fronts at once.”

Corbyn is guaranteed a fight from the press, which moved from bewildered incomprehension to apocalyptic panic, before settling on sneering contempt. This attitude is not confined to the rightwing, billionaire-owned, media — every major newspaper opposed Corbyn’s leadership bid. His first days in the job gave a taste of what will follow: when he chose not to sing the national anthem at a remembrance service for the Battle of Britain, headlines screamed: “CORB SNUBS THE QUEEN” (2).

“God knows what they’ll come up with to denigrate him,” says Mark Steel. “They’ll be extraordinarily vicious. But the defence against it is the movement. Suddenly it becomes harder to tell those lies if you’ve got a million people saying ‘Oh, that’s not true, you know’”. Corbyn has spoken of “converting the Labour Party into much more of a social movement” (3). His lack of support among MPs may force him to make good on those words, just as the hostility of the press demands the development of a dynamic social media strategy.

“If all of us who voted for Corbyn don’t now get involved, either join the Labour Party or lean in, then this whole campaign will be nothing more than a Facebook ‘like’,” warns the singer Billy Bragg. He wants an open, progressive alliance, a “left synergy”, perhaps involving cooperation with the Greens. Natalie Bennett, the Green Party leader, does not shut the door on the idea. “We’ve had a Labour Party that’s been pro-austerity, pro-privatisation, pro-Trident nuclear weapons and military interventionism. Those are all things the Green Party is opposed to; they’re all things that Jeremy Corbyn is opposed to. We’ll have to see what kind of Labour Party emerges… Everything is changing.”

The fact that the anti-austerity movement in Britain has been realised inside an established party might seem like a shortcut, an enormous advantage. But it brings with it great handicaps. The Labour Party was not designed to confront the state. It is not an insurgent organisation like Syriza. To succeed, Corbyn will have to transform it into an activist party capable of sustaining the incredible upsurge that has lifted him to the leadership. If the excitement generated over the last few months can be transmitted to the wider public in the coming years, and if events go his way, Corbyn stands a chance. But if the movement dissipates, and he is forced to rely on the old centres of power, he will be crushed.