British Prime Minister Boris Johnson on Friday faced questions about his leadership after weeks of controversy culminated in a crushing by-election defeat in a constituency never previously lost by his Conservative Party.

His ruling Tories had held the seat in North Shropshire, central England, by a massive majority just two years ago, but saw that wiped out by the Liberal Democrats in a vote on Thursday, a historic defeat set to intensify the mutinous mood among Conservative MPs.

Johnson, 57, was already reeling from a series of scandals amd setbacks and around 100 of his lawmakers rebelled in parliament Tuesday against the government's introduction of vaccine passes for large events.

The UK leader's authority has also been hit repeatedly in recent weeks by claims of corruption and reports that he and his staff broke coronavirus restrictions last Christmas, while a new surge in Omicron cases have added to a sense of crisis.

The government reported nearly 89,000 new infections Thursday, the second consecutive record daily tally.

The Tories lose the safe rural seat, won by 23,000 votes in 2019, by almost 6,000 votes, as the Lib Dems mustered a swing of 34 percentage points -- the seventh biggest in by-election history.

"The people of North Shropshire have spoken on behalf of the British people," winning candidate Helen Morgan said in her victory speech.

"They have said loudly and clearly: 'Boris Johnson, the party is over'.

"Your government, run on lies and bluster, will be held accountable. It will be scrutinised, it will be challenged and it can and will be defeated."

'They gave us a kicking'

The shattering defeat drew an immediate backlash from some Tory MPs and predictions that letters of no-confidence in their leader could be dispatched to trigger an internal party vote to remove him.

The same process saw his predecessor Theresa May ousted in mid-2019 after MPs, including Johnson, voted against her Brexit deal in parliament.

"The Conservative Party has a reputation for not taking prisoners. If the prime minister fails, the prime minister goes," long-serving lawmaker Roger Gale told BBC Radio.

"Mr Johnson has to prove that he's capable of being a good prime minister and at the moment it's quite clear that the public don't think that that's the case."

However, others cautioned that surging Covid infections could buy the prime minister time to turn around his fortunes.

"It doesn't meant the end, and it certainly doesn't mean leadership challenges," said Charles Walker, the vice-chairman of the party's 1922 Committee which collates no-confidence letters and manages any leadership contest.

"The Conservative Party is not going to have a leadership challenge as we are heading into potential further restrictions around Covid, and difficulties around Covid."

Party chairman Oliver Dowden, also a government minister without portfolio, said North Shropshire's voters were "fed up and they gave us a kicking" but that "we've heard that loud and clear".

"The prime minister is an electoral asset for the Conservative Party," he insisted to Sky News.

"On the big calls, (he) has the vision and the direction to get us through this difficult period."

'Voted tactically'

The atmosphere before the North Shropshire vote was a far cry from May, when the Conservatives swept to their own unprecedented by-election victory in the northeast England seat of Hartlepool on the back of a successful vaccine rollout.

But the virus is once again dominating British life and the arrival of the Omicron variant has again deepened the gloom before Christmas, just when the prime minister's authority has been weakened.

Britain is also suffering spiralling inflation as a result of big borrowing during lockdowns, high energy prices and bottlenecked supply chains. Tax rises also loom from next April.

Johnson -- who won voters' overwhelming backing in 2019 on his promise to "Get Brexit Done" -- has been dogged by controversies since early last month.

It began with his unsuccessful attempt to change parliament's disciplinary rules to spare North Shropshire MP Owen Paterson a suspension after he was found to have breached lobbying rules.

Paterson, who had held the seat since 1997, then quit, forcing Thursday's vote.

That crisis, though, was soon eclipsed by reports that Johnson and his staff broke Covid rules last year by holding several parties around Christmas -- just as the public were told to cancel their festive plans.

The Lib Dems appeared to have been helped Thursday by supporters of the main opposition Labour party lending them their votes, in a bid to wrestle the seat from the Tories.

"I'm sure there were lots of Labour voters who voted tactically," jubilant Lib Dem leader Ed Davey said.

"That's just what voters want to do -- it's their democracy."