Britain's ruling Conservatives on Friday held the former seat of ex-Prime Minister Boris Johnson, but saw hefty majorities in two other seats blown away as scandals and high inflation took their toll.

Rishi Sunak was expected to become the first prime minister to lose three parliamentary seats in one day, but was spared that humiliation due to a narrow victory in the west London seat of Uxbridge and South Ruislip.

While that result may have offered the embattled Sunak some relief, 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 next year.

The main opposition Labour Party are currently enjoying double-digit poll leads and are poised to retake power for the first time in over a decade. It has now won six by-elections since March of last year, with two of those seats captured from the Tories.

The Tories, however, had been expected to lose Johnson's former seat of Uxbridge and South Ruislip, but won by 13,965 votes to 13,470, delivering a blow to Labour leader Keir Starmer and London's Labour Mayor Sadiq Khan.

Sunak, who has not been visible on the campaign trail, sought to project a business-as-usual image Thursday but privately briefed backbench MPs to expect the worst.

Sunak became prime minister last October 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.

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

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