Defeat in the Brecon by-election has stymied any plans Boris Johnson had for an early general election

The Liberal Democrat victory in Brecon and Radnorshire makes the prime minister’s Brexit problem harder to solve

As Boris Johnson approaches the moment of truth on Brexit, he has one fewer vote in the House of Commons.

Jane Dodds, the new Liberal Democrat MP for Brecon and Radnorshire, will take Jo Swinson’s party up to 13 MPs, and add one to any vote for remaining in the EU or against a no-deal Brexit.

Last night’s result will also discourage the new prime minister from an early dash for a general election. The Brexit Party candidate, Des Parkinson, won only 10 per cent of the vote but it was more than enough to deny the Conservatives the seat.

Unusually, because an opinion poll was carried out in the constituency before Johnson became prime minister, we have some idea of the size of the “Boris effect”.

A poll by Number Cruncher Politics taken 10-18 July put the Brexit Party 10 percentage points higher than last night’s result, and underestimated the Conservative vote by 11 points.

The survey got the winning Lib Dem vote exactly right, on 43 per cent, so it suggests the effect of Johnson becoming prime minister was to shift about half the Brexit Party’s 20 per cent share of the vote to the Tories. This is a big swing, but not enough to make it safe for Johnson to call a general election.

On the other hand, the result will add to the righteous indignation felt by some of Johnson’s supporters, who blame Theresa May for allowing Chris Davies, the Conservative candidate, to stand again.

The by-election was caused when he was unseated as the MP by a petition signed by 19 per cent of his constituents, after he pleaded guilty to expenses fraud. If we assume that all 19 per cent voted against him, on yesterday’s 60 per cent turnout, that means Davies started the campaign with 32 per cent of the vote already against him.

Although Davies remains popular with local Tories, it is not hard to imagine that a different candidate – someone who was not a “conviction politician” – could easily have closed the 4 per cent gap with the Lib Dems.

As it is, instead of hailing a by-election triumph that confirmed his vote-winning stardust, the new prime minister will be forced to brush aside the defeat as a legacy from his predecessor. He knows the result makes the Brexit deadlock in the Commons just a little harder to break.

In a constituency that reflected the nationwide vote on Brexit – Brecon and Radnorshire voted to leave the EU by 52 per cent in 2016 – yesterday’s by-election was another snapshot of a nation divided down the middle. Between them, the Conservatives, the Brexit Party and Ukip (which won less than 1 per cent of the vote) won 50.1 per cent.

Yesterday’s vote makes it slightly more difficult for Boris Johnson to push his “do or die” Brexit through parliament, which may, paradoxically, make a general election after October more likely.