Two years ago this month, MPs felt the tremors of a political earthquake. The 45 per cent of Scots who voted for independence had driven a surge in SNP support. Five months later, in the general election, old loyalties dissolved. Forty Scottish Labour MPs and ten Lib Dems were swept away.

The referendum realigned Scottish politics along nationalist and unionist lines. The Conservatives, once considered irrelevant, acquired new purpose as the SNP’s antithesis. Labour was pushed to the margins.

At Westminster on 5 December, MPs asked whether another tectonic shift was under way. That afternoon, Sarah Olney, the Liberal Democrat who overturned Zac Goldsmith’s 23,015 majority in the Richmond Park by-election, was sworn in to parliament. Like the Scottish Conservatives, the Lib Dems had been the subject of derision. But by adopting a resolutely anti-Brexit stance they ended their political exile. In a seat where 72 per cent of people voted Remain, the pro-Leave Goldsmith was caught on the wrong side of his constituents.

Three days before Olney’s election, the new Ukip leader, Paul Nuttall, declared it was his party’s mission to “replace Labour”. In a mirror image of the Lib Dems’ strategy, the Liverpudlian aims to unseat pro-Remain MPs in pro-Leave constituencies.

There is reason for caution in predicting Scottish-style ruptures. Brexit is a less defining issue than independence (turnout was 72.2 per cent in the former vote and 84.6 per cent in the latter). The SNP has formed a devolved government since 2007, allowing it to claim the mantle of incumbency as well as insurgency. The Liberal Democrats, punished for coalition in 2015, and Ukip, with a sole MP, cannot replicate this feat.

Though it felt churlish to say so following Olney’s triumph, by-elections are a historically poor indicator of general election results. In 2013 the Lib Dems hailed their victory in Eastleigh as proof that most of their 59 MPs could defy electoral gravity. Only eight did (Eastleigh’s was not among them). In 2014, after two Ukip by-election victories, excitable commentary suggested that the party could win as many as 30 seats. It won one. Supporters of both parties defected to the Conservatives when faced with the prospect of Labour taking power.

However, there are plausible reasons why the next election could upset these precedents. Brexit is a process, not an event. It will define UK politics for a decade or more. The next election could become a de facto second referendum. The Liberal Democrats will speak for aggrieved Remainers, Ukip for “betrayed” Leavers. Both Conservative and Labour MPs fear an electoral price.

“Remainers feel that they’ve been sidelined, pushed to one side, made to feel small,” Anna Soubry, the former Tory business minister, told me. She lamented that Theresa May’s “wonderful” words when she entered Downing Street were “undermined” by her “hard Brexit” conference speech. Soubry warned of the next election: “When 2020 comes along, those aged 15, 16, 17 now will be able to vote. A large number feel that they have had their future stolen by an older generation.”

To some, the potential for Lib Dem gains appears limited. Only two of their top 30 Tory targets (Hazel Grove and Lewes) are Remain seats with Leave MPs. But Conservatives worry that the Lib Dems could triumph by forging a pro-EU coalition of Labour and Green supporters. Under first-past-the-post, as the SNP can testify, seats can be won with significantly less than 50 per cent of the vote.

By far the greatest anxiety, however, is felt among Labour MPs. “We face a tougher electoral map than at any other time in our history,” Jonathan Reynolds, the shadow Treasury minister, told me. The party remains marooned in Scotland and fears a three-way squeeze in England between the Tories, Ukip and the Lib Dems. Labour’s poll ratings, which last month averaged 29.5 per cent, were described as “dire” by its general election co-ordinator, Jon Trickett, at an NEC meeting on 22 November. Jeremy Corbyn’s ally warned that the party would have to “defend some seats” at the next election, rather than focusing on targets alone.

MPs speak of a gnawing sense that Labour is the party of the past. In a less tribalistic age, when voters are no longer defined by their work, it risks political redundancy. Across Europe, social democracy appears in structural, not merely cyclical, decline.

Rather than pitching solely to Remain or Leave voters, Corbyn’s team intend to target both through a vision of “the kind of country we want to live in”, and a focus on jobs, living standards and the economy (though they do not rule out supporting a second referendum). Others, feeling the electoral ground shift beneath them, advocate more radical action. After Richmond, Clive Lewis, the shadow business secretary, reaffirmed his call for a “progressive alliance” under which Labour would not stand candidates in certain seats. Reynolds, a fellow pluralist, told me: “We can’t pretend that people have the class allegiances of the past.”

Another group, in the words of one MP, will “follow the Lib Dem playbook, treat the party as a franchise and run ultra-local campaigns”. Leaflets will be free of references to Corbyn and national policy. “You’ve got to cut the mother ship adrift and row yourself to safety.”

At the very moment that the UK is preparing to leave the EU, its politics has never appeared more European. Britain’s fractured opposition of socialists, nationalists, liberals and greens has long been common on the continent. Amid this tumult, Conservatives hope that Theresa May will predominate in the manner of Germany’s Angela Merkel. In the absence of a Labour recovery, they anticipate at least another decade in government.