BLAME George Dangerfield. It was the Anglo-American journalist who first pathologised the end of Britain’s two-party system in “The Strange Death of Liberal England”, a commanding tale of the Liberal Party’s fall in the early part of the 20th century. To future generations he bequeathed an establishment too ready to see each political twist as proof of a new realignment. In 1993 the opposition’s fourth successive defeat inspired a tome called “The Strange Death of Labour England?”. Twelve years and two Labour landslides later came “The Strange Death of Tory England”. The Conservative-Liberal Democrat coalition of 2010 brought a flurry of fresh predictions of an end to the two-party order, before the 2015 election went off-script and produced a Tory majority. Such times bring out an epochal chauvinism in commentators: a belief that this moment, the writer’s own era, is pivotal. Most “strange deaths” since Dangerfield have met a strange death of their own: fatal collision with the next big political event.

So your columnist takes his credibility into his hands when he hereby declares the strange impending death of the two-party order. The pollsters at ICM now put Theresa May’s Conservative Party on 44%, one point below its highest-ever showing. Brexit has pushed the sort of red-trousered UK Independence Party (UKIP) supporters who quit the Tories under David Cameron back into the fold. And with the Lib Dems ejected from power, the governing party can now confidently span the spectrum from liberal conservatism to right-wing populism. On the right this feels like anything but a time of fragmentation.

But on the left the story is different. Labour has not yet grasped the crushing electoral toxicity of Jeremy Corbyn. New debates over Brexit and immigration are scratching at scabs formed after last year’s election. The announcement on December 6th of an early re-election campaign by Len McCluskey, the Corbynite chief of Unite, Britain’s biggest union, could be the latest shot in a cold war that later turns hot and pulls Labour apart. Then there is the election, on November 28th, of Paul Nuttall as the new UKIP leader, on a platform to challenge Labour in its post-industrial heartlands. And lastly comes the resurgence of the Lib Dems in metro-liberal Britain; their new appeal was revealed at the Richmond Park by-election on December 1st, when Labour’s vote fell from 12.3% to 3.7%. All of which points towards a future in which the left-of-centre vote in England splits between Labour, UKIP and the Lib Dems, with each party taking some 15%. To the north, the Scottish National Party competes on similar leftish ground.

The underlying trends are, however, not exclusive to the left. They transcend Labour’s suicidal enthusiasm for Mr Corbyn. The vote share of the two main parties has fallen from 96.8% in 1951 to 67.3% in 2015. Like electorates elsewhere, today’s Britons are less deferential and tribal than they once were. Meanwhile, where once class differences motivated a politics of left v right, now educational differences motivate a politics of open v closed. In the long term that will affect the Tories as much as Labour. For while Mrs May’s all-things-to-all-people stance on Brexit unites her coalition of London merchant bankers, Rutland farmers and Essex entrepreneurs, the details of the coming negotiation will drive wedges between them. Just as the initial vote to leave the EU has split Labour’s coalition of Manchester students, Teesside steel workers and Hackney nurses, the realities of Brexit politicise and prioritise the differences between various sorts of Conservatives.

At this point people usually cite the reason why British politics is not an efficient market: the first-past-the-post electoral system by which the country trades responsiveness for stability. As Maurice Duverger, a French sociologist, first observed, such a plurality-based system tends to produce two monolithic parties through elimination (small parties with wide support cannot win individual constituencies) and fusion (they merge to obtain the critical mass needed). Yet “Duverger’s Law” is a product of the 1950s. Back then, seats were fairly uniform, their politics overwhelmingly a function of the ratio of white-collar workers to blue-collar ones. Britain was a country of many accents but was one political universe.

Layered on top of this left-right politics, the new open-closed sort makes for a more complicated map: multiple political universes, each with its own law of physics. Wealthy university towns, fading big-city suburbs, poor working-class towns with good connections, decaying seaside resorts; each falls differently on a two-dimensional spectrum combining class (economics) and education (culture). For the Tories and Labour, used to the simple left-right spectrum, this makes life harder. It loosens voters’ allegiances. It creates openings for parties that can adapt to specific sorts of seat. In a system designed for generalists it encourages specialisation. Seen in this light, Richmond Park’s lurch into Lib Dem hands hints at how British politics will now evolve.

Que PR será

And the process could prove self-reinforcing. One critic of Duverger’s Law is Josep Colomer of Georgetown University. He argues that the causality runs in the opposite direction: party systems dictate electoral systems and thus, when two-party systems start to fragment, the pressure for proportional representation (PR) grows. Early signs of this may be visible in Britain: the Lib Dems and UKIP—both confident in a new period of open v closed—both campaign vocally for PR. If they succeed, the result will be a further explosion of political diversity and competition.

Nothing in this unpredictable age is certain. Yet most fundamentals say Britain is shifting away from Duverger’s two-party world to the fragmenting landscape described by Mr Colomer. This may become clear in the time it takes Britain to quit the EU. Or the process may take longer, the big two parties losing their monolithic status only slowly and haltingly. Either way, Britain is set for the strange death of the strange deaths of strange deaths.

Economist.com/blogs/bagehot