How important is the Brecon and Radnorshire by-election?

Politics Explained: A win for the Lib Dems today will be a significant gain for Remainers, and for all those opposed to a no-deal Brexit

Chris Davies has been behind the Lib Dems’ Jane Dodds in polling (PA)

If the Conservatives lose the seat in Wales, as expected, it will reduce Boris Johnson’s majority to just one. Together the Conservatives and the Democratic Unionist Party will hold 321 seats, while other parties and independent MPs will hold the other 320.

The position isn’t quite as precarious for the new prime minister as it seems, however. In most cases, Johnson will be able to rely on the support of Charlie Elphicke, the MP for Dover, who had the Tory whip removed this month when he was charged with sexual assault, an accusation he denies.

The reason Jeremy Corbyn held back from tabling a motion of no confidence in Johnson’s government last week was that it was certain to be defeated: in addition to Elphicke, Sylvia Hermon, the independent unionist MP, voted with Theresa May in the last vote of no confidence in January, and Ivan Lewis and John Woodcock, former Labour MPs, abstained.

Yet the arithmetic of a future vote of no confidence, if it were designed to stop Johnson pursuing a no-deal Brexit, is unpredictable, and every single vote could count.

If Jane Dodds, the Liberal Democrat candidate and the party’s leader in Wales, wins the by-election, it will tilt the balance in the House of Commons a bit further against a no-deal Brexit.

So what is going to happen? Only one opinion poll has been carried out in the constituency, by Number Cruncher Politics, which put Dodds on 43 per cent, 15 points ahead of Chris Davies, the Tory candidate, whose conviction for expenses fraud caused the by-election.

Des Parkinson, the Brexit Party candidate, was in third place on 20 per cent, with Labour’s Tom Davies trailing on 8 per cent.

But that poll was carried out between 10 and 18 July, a week before Johnson became prime minister, so it is possible that Davies might benefit from the national “Boris bounce” in the Tories’ favour. In national opinion polls there has been a shift of about 5 per cent of voters from the Brexit Party to the Tories. That is not going to be enough to hold the seat, which makes the Tories’ decision to allow Davies to stand again – after he was dismissed by a petition signed by 19 per cent of his constituents – all the more curious.

The by-election has also been hailed as a test of a common front among the Remain parties, because Plaid Cymru and the Green Party decided stand aside to give the Lib Dems a free run. As Plaid Cymru won a mere three per cent of the vote in the 2017 election, and the Greens didn’t have a candidate, this wasn’t such a great sacrifice – and in any case the Lib Dems were well placed to contest the seat, having held it between 1997 and 2015.

All the same, a Lib Dem win today will be a small but significant gain for Remainers, and and for all opponents of a no-deal Brexit, despite the constituency having voted, in line with the nation as a whole, by 52 per cent to leave the EU in the referendum.