Tory by-election defeats will be seen as more nails in coffin of Rishi Sunak's hopes of general election win

Whatever the result of the three by-elections, the Tories are already the losers

Voters go to the polls to choose new MPs in three by-elections on Thursday – and the Tories are braced to lose them all.

If that is how it turns out, the results will not do much to dent the party’s large Commons majority, but they will nevertheless be hugely significant and be seen as three more nails in the coffin of Rishi Sunak’s fast-diminishing chances of winning the next general election, expected next year.

One of the seats at stake is Boris Johnson’s former constituency of Uxbridge and South Ruislip, in outer London, where he had a 7,000 majority. The ex-prime minister quit as an MP rather than face suspension from the Commons after the privileges committee concluded he had repeatedly misled parliament over Partygate.

Shadow chancellor Rachel Reeves with Labour activists campaigning in the Uxbridge and South Ruislip by-election which takes place on Thursday. Picture: Stefan Rousseau/PA Wire

Another of the by-elections is in the North Yorkshire seat of Selby and Ainsty, where Johnson ally Nigel Adams resigned after he was blocked from receiving a peerage in Boris Johnson’s resignation honours list. And the third is in the Somerset constituency of Somerton and Frome where Tory MP David Warburton resigned, after admitting taking cocaine and being accused of sexual harassment, which he denied.

Labour is hoping to seize Boris Johnson’s old seat – the eight-point swing needed should be achievable, given the party’s lead in national polls. The Tories there are trying to make the contest a referendum on the controversial expansion of London’s Ultra Low Emission Zone, but Labour believe concerns over the cost of living are more potent.

Selby and Ainsty looks a tougher nut for Labour to crack – there was a Tory majority of over 20,000 at the last general election and Labour needs an 18.5 per cent swing to win. But such is the disillusionment with the Government that Tories privately appear resigned to defeat.

In Somerton and Frome, where the Tory majority was 19,000, it’s the Lib Dems who are seen as in pole position. The party held the seat from 1997 until 2015 and scored a notable victory in a by-election in nearby Tiverton and Honiton just over a year ago, when it overturned a Tory majority of 24,000.

By-elections are sometimes dismissed as irrelevant, just a “protest vote” – they’re not about choosing a government and are not a reliable indicator of how people will vote in a general election. All that is true, but it is precisely the opportunity for people to have a protest vote that gives by-elections their power and significance. It is a barometer of the public mood, a test of government popularity. And their significance is increased the closer to the next general election they happen.

By-elections are sparked by a variety of circumstances – sometimes by an MP’s death, perhaps a move to the House of Lords, or resignation over some scandal. But it is unusual to have by-elections which appear to be part of a party’s internal civil war, as in two out of the three contests on Thursday. Boris Johnson and Nigel Adams were not forced to quit – they did so in full knowledge of the likely damage it would cause Mr Sunak and his government.

Losing three by-elections on one day would be a major blow for the Tories. But in a sense, whatever the result, they are already the losers.