British Prime Minister Boris Johnson on Friday suffered a by-election defeat in a constituency that has always been a sure-win for his Conservative Party, a result which raises serious questions about his leadership.

His party won the seat in North Shropshire, central England, by a large margin in 2019, but the Liberal Democrats wiped it out in Thursday's vote, intensifying mutiny among Conservative MPs.

Johnson was already reeling after over 100 of his MPs protested the government's introduction of vaccination passes for large events in parliament on Tuesday.

Accusations of corruption and revelations that he and his staff violated coronavirus limits last Christmas have hammered the UK leader's authority in recent weeks.

Weeks of poor headlines transformed what would have been a routine victory in the safe rural seat — won by 23,000 votes just two years ago — into a landslide defeat of almost 6,000 votes, while rising virus infections increased the sense of panic.

On Thursday, the authorities reported roughly 89,000 new illnesses, the second consecutive daily high.

Helen Morgan, the winning candidate, claimed that voters had delivered Johnson a "loud and clear" message that "the party is over."

"Your government, run on lies and bluster will be held accountable. It can and will be defeated," she vowed.

 'Slap in the face' 

In the event of defeat, additional MPs are likely to file letters of no confidence in their leader, potentially leading to an internal party vote to oust him.

His predecessor, Theresa May, was removed from office in mid-2019 when MPs, including Johnson, voted against her Brexit plan in parliament.

The Liberal Democrats looked to have benefited from the votes of followers of the main national opposition Labour Party.

"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." 

Gloomy outlook 

The ambiance preceding the vote was a far cry from May when the Conservatives won an extraordinary by-election victory in Hartlepool, in northeast England, thanks to a successful vaccine rollout.

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

It is worth noting that Johnson has been dogged by controversies since early last month.

It all started with his failed attempt to change parliament's disciplinary processes to prevent North Shropshire MP Owen Paterson from being suspended after he was found guilty of breaking lobbying rules.