The votes are one of few remaining opportunities to gauge public support before a general election due next year, with the main opposition Labour Party enjoying poll leads of around 20 per cent and poised to retake power for the first time in over a decade.

Labour, under its leader Keir Starmer, won local council elections in early May across swathes of England, with Sunak’s Conservatives suffering steep losses in his first major electoral test since taking power last October.

The opposition has won five by-elections since March last year, but only one of those seats – Wakefield, in Yorkshire – was snatched from the Tories.

Labour is now aiming to emulate that June 2022 feat in nearby Selby and Ainsty, where Nigel Adams quit as Conservative MP last month after failing to be nominated for a peerage by ex-prime minister Boris Johnson.

Labour is also eyeing victory in Johnson’s northwest London constituency of Uxbridge and South Ruislip, after the scandal-tarred former leader himself resigned as an MP last month and triggered the ballot.

He quit after learning a cross-party parliamentary committee had concluded he deliberately lied to lawmakers about lockdown-breaking parties during the Covid pandemic and had recommended a 90-day suspension.

UK opposition wins special election in blow to Sunak’s party

The Liberal Democrats are intent on overturning a 20,000-strong Tory majority in Somerton and Frome, after its Tory MP David Warburton stood down following an admission of cocaine use.

Sunak, who became prime minister following the disastrous 44-day tenure of predecessor Liz Truss, initially succeeded in stabilising financial markets panicked by her radical tax-slashing agenda.

But the 43-year-old former finance minister has struggled to reverse his party’s declining fortunes, which first set in during the so-called “Partygate” scandal under Johnson.

Sunak’s turnaround efforts have in part been hobbled by persistently high inflation, which in recent months has spooked the markets once again.

With interest rates at their highest in 15 years, pushing mortgage and other borrowing costs ever higher, the worst cost-of-living crisis in a generation is showing few signs of abating.

Sunak kicked off the year by making five key vows to voters, including halving inflation, growing the economy and cutting waiting times within the overstretched National Health Service (NHS).

He has made little headway on most of the pledges, and there are persistent fears the UK will tip into recession this year as the high interest rates constrain spending.

Sunak’s net favourability has fallen to its lowest level (-40) since he entered Downing Street, with two-thirds of Britons saying they have an unfavourable view of him, according to YouGov.

His allies were downplaying the party’s prospects on Thursday, while insisting there was still time for a Tory revival before the next national contest.

“As you’ve heard before, by-elections for incumbent governments are very difficult,” Sunak’s press secretary told reporters on the eve of the by-elections, adding that the Conservative Party was “most focused” on the general election.

Additional reporting by dpa, Reuters