Britain's ruling Conservatives lost two more parliamentary seats to Labour in by-elections Friday, highlighting the mountain Prime Minister Rishi Sunak must climb to win a general election due this year.

The losses capped a dire week for the UK leader, struggling to revive support for his beleaguered party, as official data showed Britain is in recession after economic contraction for two successive quarters.

In power since 2010, the Conservatives are widely tipped by pollsters to lose the nationwide vote that 43-year-old Sunak has said will be held in the second half of the year.

The main Labour opposition secured its second largest by-election swing away from the Conservatives in one of Thursday's contests, held after a Tory MP quit and another faced a recall petition over bullying his staff.

"People want change and are ready to put their faith in a changed Labour Party to deliver it," said its leader Keir Starmer as he hailed the "fantastic results".

Sunak said the circumstances surrounding the by-elections were "particularly challenging" but claimed that turnout of below 40 percent in both constituencies meant there "isn't a huge amount of enthusiasm" for Labour.

- Latest losses -

The by-elections highlight the struggle Sunak faces if he is to secure a fifth consecutive term in power for the Conservatives.

The party has lost a string of traditionally safe seats to Labour and the smaller centrist Liberal Democrats since winning a landslide at the last general election in 2019.

Ex-chief prosecutor Starmer and his party have enjoyed double-digit leads over the Tories in most opinion polls throughout Sunak's 15-month tenure as prime minister.

Sunak replaced Liz Truss, who was ousted after her tax-cutting economic agenda spooked markets and lost support.

The Conservatives' popularity has plummeted as Britain has endured the worst cost-of-living crisis in decades since the pandemic.

Britons have also been turned off by factional infighting and chaotic rule that have led to three prime ministers since autumn 2022.

A record 21 by-elections have now been held since 2019, many as a result of misconduct committed by Tory MPs.

Thursday's defeats in Wellingborough, central England, and in Kingswood, in the southwest, were the Conservatives' ninth and tenth losses this parliament.

They have now lost more by-elections in a single parliament than any government since the 1966-70 Labour administration of Harold Wilson, which suffered 15.

- Big swings -

Former Wellingborough Tory MP Peter Bone was suspended from parliament after an inquiry found he had subjected a staff member to bullying and sexual misconduct.

Bone's partner Helen Harrison was controversially selected as his replacement candidate in the seat, held by the party since 2005.

Labour candidate Gen Kitchen overcame a majority of 18,540 by scoring a 28.5-percent swing -- her party's second largest ever from the Conservatives in a by-election.

The vote in Kingswood, near the city of Bristol, was triggered by Chris Skidmore's resignation as an MP in protest at Sunak's plans to boost North Sea oil and gas drilling.

Labour won the seat -- Tory since 2010, but due to be abolished for the general election under the redrawing of constituency boundaries -- with nearly 45 percent of the vote.

Sunak will also be unnerved by fringe right-wingers Reform UK -- formerly the Brexit Party -- securing more than 10 percent for the first time, suggesting his party is losing voters to the right as well as Labour.

Reform's performance "possibly points to their appeal not necessarily being highly concentrated in a handful of seats," said Chris Hopkins, political research director at the polling firm Savanta.

The wins will be welcome respite for Labour, after it also endured a difficult week following the suspension of two prospective MPs over allegations of anti-Semitism.

One had been selected to contest a by-election this month, in Rochdale, near Manchester, which has been sparked by the death of a veteran Labour MP.