British Prime Minister Boris Johnson on Friday appeared on the cusp of a crushing by-election defeat in a constituency never previously lost by his Conservative Party, a result which would raise serious questions about his leadership.

Counting was still underway in the by-election in North Shropshire in central England, but Liberal Democrat MP Christine Jardine declared on Sky News that "we're not just going to win here tonight, we're going to win comfortably."

Tory MP Edward Timpson seemed to agree, telling Sky News that "I've already conceded it's been a very difficult night for us."

Defeat would be a disaster for the Conservatives, who won the seat by a massive majority in 2019, and would intensify the mutinous mood among the party's MPs.

Commentators predict Boris Johnson's position would be under threat if his Conservatives lose the by-election
Commentators predict Boris Johnson's position would be under threat if his Conservatives lose the by-election POOL via AFP / Stefan Rousseau

Johnson, 57, was already reeling after roughly 100 of his own MPs rebelled in parliament Tuesday against the government's introduction of vaccine passes for large events.

The UK leader's authority has also been clobbered repeatedly in recent weeks by claims of corruption and reports that he and his staff broke coronavirus restrictions last Christmas.

Weeks of bad headlines have turned what would normally be a routine victory in the safe rural seat into a far more fraught process for Johnson's Tories, while surging virus cases have added to a sense of crisis.

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

Ahead of polls opening in the seat of about 80,000 voters, Johnson appeared to be struggling to convince locals to stick with him, prompting predictions of a historic loss in a seat where the previous Conservative MP won a 23,000 majority in the last election.

North Shropshire is a rural constituency in central England that has always returned a Conservative MP
North Shropshire is a rural constituency in central England that has always returned a Conservative MP AFP / Paul ELLIS

Defeat would likely see more MPs filing letters of no-confidence in their leader, which could 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 Liberal Democrats appear to have been helped by supporters of the main national opposition Labour party lending them their votes.

A series of recent scandals and the arrival of the Omicron variant of coronavirus have deepened the gloom
A series of recent scandals and the arrival of the Omicron variant of coronavirus have deepened the gloom AFP / Oli SCARFF

"I'll be voting for the Liberal Democrats because I'm so offended by the performance of Johnson," Martin Hill, 68, who normally votes Labour, told AFP earlier this week.

"It'll be a tactical vote -- I want to give Johnson a slap in the face."

However, others in the small town of Whitchurch were prepared to overlook the former London mayor's transgressions.

"I think Boris Johnson's been a bit silly really... like a naughty little schoolboy," said 67-year-old Sue Parkinson, who has voted Conservative for the last two decades.

"I don't think it's enough for us to say: 'right, we want a new leader now', because I think Boris has done an excellent job."

The atmosphere is a far cry from May, when the Conservatives swept to an unprecedented by-election victory in the northeast England seat of Hartlepool on the back of a successful vaccine rollout.

But the virus is dominating British life again and the arrival of the Omicron variant has again deepened the gloom before Christmas, with the prime minister's authority seen as 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 by-election.

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.