Britain's ruling Conservatives on Friday held the former seat of ex-Prime Minister Boris Johnson but saw hefty majorities in two other constituencies blown away as voters responded to scandals during his tenure and high inflation.
Rishi Sunak was expected to become the first prime minister in decades to lose three parliamentary seats on one day, but was spared that humiliation due to a narrow victory in the northwest London seat of Uxbridge and South Ruislip.
That result, driven by opposition to Labour mayor Sadiq Khan's contentious expansion of a vehicle pollution tax to outer London, offered the embattled Tory leader some relief.
But the wiping out of his party's 19,000 majority in the Somerton and Frome seat and its 20,000 majority in the Selby and Ainsty constituency will come as hammer blows ahead of an expected general election in 2024.
"By-elections midterm for an incumbent government are always difficult, they rarely win them," Sunak told reporters Friday morning, striking a defiant tone while visiting Uxbridge and South Ruislip.
"The message I take away is that we've got to double down, stick to our plan and deliver for people... and earn people's trust for the next election."
But his Conservatives face defeat nationally next year if Thursday's results are repeated.
The Labour party took the northern England seat of Selby and Ainsty by 16,456 votes to 12,295, in one of the biggest swings to the main opposition in UK election history.
Stunning
Savouring the emphatic victory, Labour leader Keir Starmer tweeted that Selby and Ainsty had "made history".
"This incredible result shows how powerful the demand for change is," he added.
Ex-Tory MP Nigel Adams prompted the by-election by quitting after failing to be nominated for a peerage last month.
In Somerton and Frome in southwest England, the Liberal Democrats comfortably won with an even bigger shift from the Conservatives.
Winning candidate Sarah Dyke touted her "stunning and historic victory", and took aim at the "woeful government".
The contest was held after its former Tory MP David Warburton stood down following an admission of cocaine use.
The Uxbridge and South Ruislip by-election was triggered after the scandal-tarred Johnson also resigned as a lawmaker last month.
He quit after learning that a cross-party parliamentary committee had concluded he deliberately lied to lawmakers about lockdown-breaking parties during the COVID-19 pandemic, and recommended a 90-day suspension.
Sunak's Tories had been expected to lose his seat, but won by less than 500 votes, delivering a blow to Starmer and Khan.
Winning candidate Steve Tuckwell said the "number one" issue had been the mayor's expansion of the "Ulez" tax on polluting vehicles.
He warned Labour MPs in similar seats "will now be panicking".
Sunak struggles
However, the heavy defeats in the other two contests leave Sunak increasingly vulnerable, with parliament's six-week break starting Friday providing welcome relief.
Labour is currently enjoying double-digit poll leads and is poised to retake power for the first time in over a decade.
Sunak became prime minister following the disastrous 44-day tenure of predecessor Liz Truss and 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 at the overstretched National Health Service.
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.