British Prime Minister Boris Johnson's Conservative Party on Friday lost two parliamentary seats, prompting the resignation of the party's chairperson and renewing doubts about the future of the country's embattled leader.

The losses – one in the Conservatives' traditional southern heartlands and in a northern England seat won from Labour in the last election – suggest the electoral coalition Johnson brought together at the 2019 national election may be fracturing.

The transformation of Johnson from vote winner to electoral liability may prompt lawmakers to move against him again after months of scandal over COVID-19 lockdown parties and amid a growing cost-of-living crisis.

Johnson has resisted intense pressure to resign after he was fined for breaking lockdown rules at his Downing Street office, and rejected the idea that he would quit if his governing party lost the so-called by-elections.

"It’s absolutely true we’ve had some tough by-election results ... I think as a government I’ve got to listen to what people are saying," Johnson told broadcasters after the results.

"We’ve got to recognize there is more we’ve got to do ... we will keep going addressing the concerns of people until we get through this patch."

Johnson is currently out of the country in Rwanda for a Commonwealth meeting.

This month he survived a vote of confidence by Conservative lawmakers, though 41% of his parliamentary colleagues voted to oust him, and he is under investigation by a committee over whether he intentionally misled parliament.

Following the losses in Tiverton and Honiton in southern England and Wakefield in the north, Conservative Party Chairperson Oliver Dowden resigned, saying things had to change.

"Yesterday's parliamentary by-elections are the latest in a run of very poor results for our party. Our supporters are distressed and disappointed by recent events, and I share their feelings," Dowden said in a resignation letter to Johnson.

"We cannot carry on with business as usual. Somebody must take responsibility and I have concluded that, in these circumstances, it would not be right for me to remain in office."

Several Conservative lawmakers tweeted support for Dowden, saying he was not to blame for the results in messages that suggested resurgent dissent against Johnson's leadership.

Although under his party's rules Johnson cannot be challenged with a no-confidence motion for another year, lawmakers fearing for their own futures may decide to reduce the grace period to bring about another vote.

A wave of resignations from Johnson's Cabinet team of top ministers is seen as another way the prime minister could be forced out.

The next national election is scheduled to be held in 2024 but it could be called earlier.

'Go now'

The Conservatives lost a large majority of more than 24,000 votes in Tiverton and Honiton, in a deeply Conservative part of southwest England, defeated by the centrist Liberal Democrats who secured a majority of more than 6,000.

The Liberal Democrats said it was the biggest ever majority to be overturned at a British parliamentary by-election, suggesting that other Conservative lawmakers may be at risk of losing their seats in the party's southern heartlands.

Winning Lib Dem candidate Richard Foord said in his victory speech that Johnson should "go, and go now."

"With every day Boris Johnson clings to office, he brings further shame, chaos and neglect," he said.

In the separate parliamentary seat of Wakefield in northern England, the main opposition Labour party also defeated the Conservatives.

"Wakefield has shown the country has lost confidence in the Tories. This result is a clear judgement on a Conservative Party that has run out of energy and ideas," Labour leader Keir Starmer said in a statement.

Johnson led the Conservatives to their biggest majority in three decades at the 2019 national election, winning praise from his party for his ability to win in traditionally Labour-voting areas in north and central England.

However, the loss of Wakefield could indicate that his ability to win again in these areas at the next national election, expected in 2024, has also been compromised.

The by-elections were triggered by high-profile resignations of Conservative lawmakers – one who admitted watching pornography in parliament, and another found guilty of sexually assaulting a teenage boy.