THE moment, when it came, was electric. Rumours had already flashed through the crowds in Hyde Park, where Britain’s left was gathering for a pro-refugee rally. Some claimed he had taken some two-thirds of the vote. The result almost corroborated the whisper: Jeremy Corbyn, the hard-left politician whose three-decade career as MP for Islington North he had spent on the fringes of British politics, had obtained fully 59% of first-preference votes in Labour’s leadership election. Britain now has the most uncompromising opposition leader in living memory.

In retrospect, the reasons for his election were clear enough. Under Gordon Brown and Ed Miliband, Labour had ditched the centrist legacy of its three-time election winner, Tony Blair, but offered little to take its place. During the leadership campaign Mr Corbyn had filled that vacuum by presenting his party (as well as prospective members and affiliated supporters) with a simple and certain vision: a firm rejection of the policies that had propelled Labour to power under its most successful leader. Instead his campaign, predicated on the views of a noisy minority, offered a pure socialism uncomplicated by the realities of Britain in 2015. It was a vision that will yet describe the terms of the new Labour leader’s downfall.

The defining feature of the party’s new era is the massive influx of new members and other affiliates that it has experienced in the past months. Over 550,000 people were eligible to vote in Labour’s leadership election, almost three times the party’s pre-election membership and an illustration of the surge of union members, interested (mostly young) outsiders and—in a small number of cases—malicious saboteurs who joined it to vote for Mr Corbyn, expecting him to prove an electoral liability.

The result was a mandate, of sorts, greater than any enjoyed by a recent mainstream party leader. Old-timers in Labour are now waiting to see whether these thousands join their local parties and support their campaigning. Mr Corbyn and his supporters hope to convert them to engaged members; their opponents in the party doubt whether this is possible.

His election to the leadership of the Labour Party affects British politics on three levels. First, it means that the country’s main opposition leader and his team have almost no experience of front-line politics. That much was evident in the hours and days after Mr Corbyn’s election. Having run a campaign focused on equality, on September 14th he gave all the big jobs in his shadow cabinet to white, middle-aged men; most painful to his supporters was the appointment of John McDonnell, his abrasive hard-left ally, over Angela Eagle, a likeable and conciliatory soft-left figure, to the crucial post of shadow chancellor.

Many of his backers were appalled, but kept quiet. Moderates like Jamie Reed, Chuka Umunna and Emma Reynolds decided to retreat to the backbenches. Journalists who had camped outside the room in Westminster where the new leader and his team allocated jobs published an unedifying account of the overheard discussion, in which the sheer panic and lack of preparation of Britain’s new opposition leader became clear.

Second, Mr Corbyn’s triumph generates a sudden—and probably irreconcilable—gulf between Labour’s leader and most of his MPs. That was clear on September 16th, when he appeared in his first prime minister’s questions. The new Labour leader had asked for queries from ordinary voters and deployed six, one by one, during his allotted slot. Not a terrible idea, the wheeze foundered on his inability to follow up David Cameron’s answers. For much of the display Labour’s MPs sat in an embarrassed silence. They had displayed a similar demeanour during Mr Corbyn’s first address to his parliamentary party, on September 14th, when he was quizzed on his willingness to wear a red poppy to commemorate Britain’s war dead (Mr Corbyn is a pacifist and republican who—to tabloid outrage—stood silent as the rest of the congregation in St Paul’s Cathedral sang the national anthem to commemorate the Battle of Britain).

Third, Mr Corbyn’s election changes the balance in the Conservative party. None of the four candidates for Labour’s leadership had truly worried the government, but Tory strategists had rooted for Mr Corbyn nonetheless. As a result, Mr Cameron’s troops—like the bookies—take his party’s success at the next general election, due to take place in 2020, as a certainty. Moreover, they have come to acknowledge that its best chance, faced with a party led or recently abandoned by Mr Corbyn, lies in exuding stability and moderation. Thus the prime minister has spent the past weeks talking about tackling employers that do not pay the minimum wage (stealing Labour’s territory) and expanding the free-school programme (dividing Labour and forcing its leader to voice his unpopular opposition to this bid to give schools more autonomy).

George Osborne, increasingly seen as the front runner in any future Tory leadership race, benefits from this development as the obvious continuity candidate. Boris Johnson, who had been poised to challenge his party’s establishment in the event of an electoral disaster, suffers. Confronted by an eccentric who speaks his own mind, why would the Conservatives pick their own loose cannon?