AS THE result came through on the speakers, the crowd at Speakers' Corner in Hyde Park let out a giant cheer. Corks were released from bottles of fizz. Many had gathered there for a pro-refugee rally due to take place this afternoon. But many, too, had come to this traditional site of protest, debate and dissent purely in anticipation of one of the most remarkable upsets in British political history: the election of Jeremy Corbyn, perhaps the most left-wing MP in the House of Commons, as leader of the Labour Party and thus as the official leader of Britain’s parliamentary opposition. The announcement, when it came, was even more dramatic than most had expected: not only had Mr Corbyn won, but he had done so resoundingly; taking 59% of first preference-voters and thus becoming leader without needing any second-preference votes in Labour’s round-by-round electoral system.

The result illustrates two things. First is the sheer scale of the influx of new left-wing members and affiliated supporters who joined the party after the May election to back Mr Corbyn. Until the final days of the contest there had been some doubt about their propensity to use their votes. This, clearly, was misplaced. Second is the poor quality of the other candidates, most notably Yvette Cooper and Andy Burnham (Liz Kendall, the fourth and final one, deserves credit for fighting a gutsy campaign despite possessing little experience of front-bench politics). Mr Burnham, the one-time frontrunner who styled himself as the man to beat Mr Corbyn but fought an abysmal and drably sentimental campaign, came second with just 19% of first preferences.

In his acceptance speech the new Labour leader paid dignified tribute to his leadership rivals and called on the party to come together. MPs who had previously lambasted him and grimaced at the prospect of his leadership issued nice words about unity and collaboration. But the fact remains that Britain’s largest opposition party is now led by a man whose parliamentary colleagues barely know him, let alone share his politics. It convulses British politics by raising to the leadership of one of the country’s two main parties of government—one that, a decade ago, commanded the centre ground and possessed one of the most formidable election-fighting machines in the democratic world—a politician who would exist, as he has in Westminster for the past decades, as a hard-line oddball on the fringes of any Western political arena.

Immediate questions proliferate. Will Mr Corbyn bring back shadow cabinet elections, or appoint his own top team? Will the party’s conference, which takes place in two weeks, be beset by infighting or will the calls for unity translate into genuine forbearance? Will Mr Corbyn, a man with links to unsavoury governments and international groups (he calls Hamas “friends”, presented a programme for Iran’s state television and recommends Russia Today, Vladimir Putin’s international propaganda network) be made privy to sensitive information about national security, as was his predecessor as leader of the opposition, Ed Miliband?

Indubitable is that the governing Conservative party, an entire section of whose headquarters has been given over to monitoring Mr Corbyn’s statements and positions, is about to unleash the mother of all political onslaughts. At a recent summit at Chequers, his country residence, the prime minister, David Cameron, and his advisers pondered whether to let Mr Corbyn’s leadership implode organically, or whether to help it on its way.

Their conclusion was a three-part strategy. The Tories will leak negative stories to the newspapers (which are almost universally hostile to the new Labour leader) but will keep their own tone dignified in the coming days. They will, however, announce and attempt to legislate for a series of policies designed both to smoke out the new Labour leader’s opposition to popular measures and to split his party: investing in Britain’s nuclear submarine base, expanding the programme of autonomous “free schools”, tightening strike rules, clamping down on welfare payments and devolving power to the regions. Finally, they will seek to appropriate the moderate ground that Labour has vacated: already Mr Cameron has sought to use the moment to kill his party’s reputation for nastiness and antipathy to the poor by, for example, cracking down on employers who pay staff less than the minimum wage. This tripartite strategy is encompassed in the word that will pepper every Tory announcement and speech in the coming days: “security”. Tried and tested in focus groups, the term sums up everything that Conservative strategists want voters to think about the politics of defence, the economy and public services. Labour, they will parrot, is the party of national and personal insecurity.

What of Mr Corbyn’s prospects? It is just about imaginable that the new Labour leader will survive until the next general election, due in 2020. The party is tribal and bad at getting rid of sub-par leaders. Afraid of being seen as wreckers in any future leadership election, its moderates are determined not to wield the knife (at least, not soon). The scale of Mr Corbyn’s victory gives him an enormous mandate and puts to bed talk of a quick defenestration (a measure firmly in MPs’ power, if they choose to wield it) and another leadership election. Meanwhile the early indications are that he will prove realistic enough at least to try to reconcile a largely sceptical parliamentary party to his leadership: the tone of his acceptance speech was strikingly conciliatory, and there are already rumours that he will appoint a figure from Labour’s soft left (perhaps Angela Eagle or Mr Burnham), to the crucial role of shadow chancellor.

Still, it is more likely that he will quit before then. First, for all the nice words in the immediate aftermath of his appointment, chaos seems likely in the medium term. It will often prove impossible for him to reconcile a majority of his MPs and the left-wing movement that elevated him to his new post. Team Corbyn insiders concede that the greatest threat to him could come from the left, which will cry betrayal at the first compromise (it is only a matter of time until one former supporter calls him a “Tory”, the epithet applied throughout the just-finished leadership contest to those suspected of ideological impurity). Meanwhile many in the new leader’s inner circle lack both experience and influence in the wider party. Some in his shadow cabinet, like Mr Burnham, will be biding their time until he loses his footing. Many of the party’s strongest media performers will be reluctant to defend their new leader’s policies on air. The number of upcoming policy debates capable of dividing the party is substantial. They include Syria, Europe, airport expansion, government spending and immigration.

The question, then, is: how long will he last? Expect the first murmurs of mutiny to be heard this coming week, then grow through the party’s conference (though the pretence of collegiality and unity will probably last longer). But the first obvious moment of peril for Mr Corbyn will be the London, Welsh, Scottish and local elections due next May. The European election in 2019 marks another moment when he will be judged by a quantifiable performance. But the real test is this: when enough Labour MPs fear they will lose their seats at the next election and have an obvious alternative candidate around whom to rally, Labour’s new leader will be toast.

Tom Watson, the formidable party fixer and machine politician whose victory in Labour’s deputy leadership race was announced minutes before Mr Corbyn became leader, will be a crucial figure; a mediator between the leadership, the new grass roots, the party right and the dogged, long-time members on whom its ability to fight elections still rests. If your columnist had to venture a guess, he would predict that after a short-lived spike in Labour's polling numbers in the coming weeks, Mr Corbyn will be weakened by their deterioration over the following months, then by poor results in next year’s elections; he will stumble into 2017 when he will be ousted in favour of a figure from the party’s soft left (perhaps Mr Watson or Ms Eagle) capable of reconciling its different wings. Nonetheless, little store should be set by that rough forecast. British politics has seemed remarkably unpredictable, fragmentary and volatile in recent years. Never more so than today.