If the leavers, the Conservative reactionaries, the neoliberals and the ranks of Britain’s rightwing press – to say nothing of their friends Donald Trump and Vladimir Putin – had had their way, Friday would have been Britain’s first day outside the European Union since 31 December 1972. But the Halloween deadline has come and gone. Instead, largely as a result of the ruthless parliamentary exposure of Boris Johnson’s shabby political quackery, Britain remains part of Europe. Friday is therefore a day for relief and a modest celebration, not for defeat or dejection. A place in Europe, for which so many have fought so hard over the last three and a half years, remains ours. But its future now rests on the result of the general election in six weeks’ time.

Mr Johnson captured the prime ministership in July on a shamelessly false prospectus. He promised he could get Britain out by 31 October, “whatever happens”. He told his party conference that it would happen “come what may”. He said he would rather be “dead in a ditch” than ask for another extension. Enough Tory members – 90,000 mainly white, elderly men living in southern England (fewer people than the population of Tunbridge Wells) – were taken in by this for him to oust Theresa May. But, as with most of Mr Johnson’s promises, these were merely cheap words. Like Mrs May, he ran into the stubborn reality that a majority of MPs want to stop any precipitate departure from the EU. Rather than compromise, as he should have done, Mr Johnson has now bounced the Commons into a premature election.

He may have been its leader for only a little over three months, but Mr Johnson has had a major impact on his party. He has triggered and presided over a tranformation of the Tories into a rightwing nationalist party. What was once a broadly based movement of the centre-right is now a political sect, defined by a single issue, Brexit, which increasingly places the party on the wrong side of history.

The exodus this week of centrist Conservative MPs who have had enough is eloquent testimony to that. The list of the expelled and the withdrawing, who include Ken Clarke, David Gauke, Justine Greening, Dominic Grieve, Philip Hammond, Jo Johnson, Oliver Letwin, David Lidington, Nicky Morgan, Amber Rudd and Rory Stewart, adds up to both a lost generation and a lost Tory tradition. Mims Davies, the employment minister, said this week that she is quitting, and asked whether female Tory MPs are going because of “the horrid state of the discourse, the threats, the hours, the lack of time with friends and family or never being able to switch off”. The upshot, as Iain Duncan Smith boasted this week, is stark. The Tories, he said, “are the Brexit party now”.

As many have pointed out, a general election is an election about everything. Jeremy Corbyn, launching Labour’s campaign on Thursday, will fight it on austerity. The SNP will fight it on Scottish independence. In Northern Ireland, the election will, as ever, be about the union. None of these is a secondary issue. Yet Mr Duncan Smith’s words cut through the jungle of other issues to identify what this election is most irrevocably about. It is about whether the UK will leave the EU and end its commitment to Europe, or whether it will not.

If the Conservatives form the next government, Mr Johnson will move quickly to get his Brexit deal into law. Yet Mr Johnson’s deal is worse than Mrs May’s and far worse than Britain’s current terms of membership. By 2029 the economy would be 4% smaller than it is forecast to be if Britain remains. Scotland could be pushed out of the UK and the Irish peace process destroyed. The Tory right, strengthened by this week’s retirements, will be within touching distance of the small-state, light-regulation Britain they crave. These things could be the realities of 2020s Britain if Mr Johnson wins next month. The task on 12 December is to stop him.