Nigel Farage's Brexit Party was the big winner in Britain's E.U. elections, winning 29 of the 73 available seats. (Peter Summers/Getty Images)

Ryan Bourne is the R. Evan Scharf chair for the public understanding of economics at the Cato Institute and was formerly head of public policy at the Institute of Economic Affairs in London.

A tumultuous few days in British politics ended over the weekend with another political earthquake.

Nigel Farage’s new Brexit Party was declared victorious in the country’s European Parliament elections, winning 31.6 percent of the vote and 29 of the 73 available seats. A concurrent revival of the overtly anti-Brexit Liberal Democrats (20.3 percent) saw the two traditional parties — Labour and the Conservatives — trailing in third and fifth place, respectively.

Alongside Theresa May’s recent resignation as Conservative leader and prime minister, one might be tempted to conclude that an unexpected political revolution is upon us. But the results were not novel. They simply reflect Westminster’s main parties’ inability to mirror and harness the divisions that rose from the 2016 referendum.

Leaving the European Union is now the central cleavage of U.K. politics. Yet neither of the main parties has swung unequivocally to represent either Leavers or Remainers. In making E.U. exit conditional on a withdrawal deal passing Parliament (the Conservative government) or not fully committing to a second referendum to reverse Brexit (Labour), the old parties are getting steamrollered by those with less ambiguous pro-Brexit or pro-Remain positions.

Behind the headlines, the public is still split. Though it’s dangerous to aggregate vote shares for multi-issue elections, around 44 percent of voters backed parties wanting to deliver some form of Brexit, while just over 40 percent supported parties willing to abandon it (how Labour’s 14.1 percent vote share should be considered is anybody’s guess, given the party’s unclear Brexit position). The key insight from party results, though, is that trying to straddle any sort of “middle-way” coalition is costly electorally.

The Conservatives’ collapse was the most dramatic, plummeting to a pathetic 9.1 percent vote share and losing 15 of the 19 E.U. Parliament seats won in 2014.

The reason is obvious. The Tories’ polling numbers collapsed in early March when it became clear they wouldn’t deliver Brexit on time, having failed to obtain parliamentary approval for the E.U. withdrawal treaty that the government had negotiated.

May concluded that leaving without a deal on the scheduled March 29 deadline would be so disastrous that delaying exit until October was preferable. Her hope was to win over more members of Parliament in the interim.

That decision backfired spectacularly. Ex-UKIP leader Farage reentered politics bemoaning Conservative betrayal. With vocal Brexiteers in her party seething, May pivoted to seek Labour votes to get her unpopular treaty through Parliament. Her concessions to win them over hemorrhaged 42 Conservative MPs, who publicly switched to oppose her deal. She eventually realized what most had known for months: There was no route to her delivering Brexit.

These results will therefore embolden Conservatives who believe the party must embrace Brexit unconditionally. Leadership candidates such as ex-mayor of London Boris Johnson and ex-Brexit secretary Dominic Raab will correctly diagnose that further delay will precipitate catastrophic electoral damage. Farage has already promised Brexit Party candidates for every seat in any future Westminster election.

These pro-Brexit Tory leadership runners will argue, too, that preparing for a “no-deal Brexit” is the only potential means of pressuring Brussels to revise the current agreement (which has been rejected three times in “meaningful votes” by Parliament).

On both counts, they are surely right. But a catch remains: Parliament opposes leaving without a deal. A new prime minister could theoretically ram Brexit through if his or her party remained loyal, but that loyalty clearly cannot be taken for granted.

Many Conservatives MPs still believe a no-deal Brexit will trash the party’s reputation for economic competence, destroying it electorally. This crowd of Remainers and “soft” Brexiteers has implied that it could even side with Labour in a no-confidence vote to bring down any government that opts for “no deal.”

Whether that threat is credible is up for debate. Voting no confidence could cost MPs their party memberships and probably their parliamentary seats. They would risk putting a hard socialist Jeremy Corbyn government in power, too. But without a Conservative majority in Parliament, any new prime minister can’t afford to lose support. If these MPs truly believe “no deal” would deliver Corbyn anyway, enough might gamble to stop it.

In the end, such divergent views cannot happily coexist. Yet significant minorities of MPs in both the Conservative and Labour parties are loath to cede their parties becoming full-on Leave or Remain entities, whether out of electoral self-interest or calculation, or because of ideological discomfort with those visions. Some Conservative leadership hopefuls clearly wish that Brexit would just go away entirely, and politics return to normal.

But the European Parliament election results add evidence that a political realignment continues apace, and that failing to pick a side and deliver has consequences. The parties look set to self-sort into overt Leave and Remain camps, or perish. With their leadership contest starting now, these results put the ball in the Conservatives’ court for the first move. It’s likely they will go “all-in” on Leave.

Read more:

Anne Applebaum: Amid fractures, Europe is becoming a single political space

Anne Applebaum: Yes, Europe’s far right is gaining strength. But so is the resistance.

Andrea Kendall-Taylor and Alina Polyakova: Populism and the coming era of political paralysis in Europe

The Post’s View: At least Theresa May tried to fix Britain’s mess. How many other politicians there can say the same?