Voters went to the polls on Thursday for two new British lawmakers, with the opposition Labour Party expected to win parliamentary seats in central and southwestern England in yet another blow to Prime Minister Rishi Sunak's Conservatives.

The Conservatives have done little to win over voters in Wellingborough in central England and Kingswood in the south west, preferring to focus on Sunak's bid to regain ground across the country before this year's national election.

But defeats in the so-called by-elections will do little to silence Sunak's critics, who fear the governing party faces an all-but wipe-out at the national election, which the prime minister says he expects to come in the second half of the year.

The British leader has pinned his hopes on having time to close the large gap with Labour in the polls and to capitalise on the difficulties the opposition party has had over anti-Semitism allegations and its now-scrapped green spending target.

"It's been a rocky week for the Labour Party, but our markets suggest they are still on course to claim a convincing victory in both the Wellingborough and Kingswood by-elections this Thursday," said a spokesperson for bookmakers William Hill.

The results are expected to come in the early hours of Friday.

While Labour sent many of its lawmakers and activists to campaign in both places, the Conservatives have had a muted presence, with many lawmakers concentrating more on trying to hold onto their own seats before the national election.

The Conservatives had held large majorities in both seats. The contest in Wellingborough was triggered after the former member of parliament was forced out over a bullying and harassment scandal, while in Kingswood, former minister Chris Skidmore resigned over Sunak's climate change policies.

Labour leader Keir Starmer faced criticism this week for not moving immediately to censure a Labour candidate in a separate vote who was recorded espousing conspiracy theories about Israel.

But the governing party has also not been without its issues -- data on Thursday showed the economy had slipped into recession in the second half of 2023, a challenge for Sunak who has made boosting economic growth a main pledge before the national election.

Labour was keen to manage expectations as voting took place.

"Labour is really up against it in these by elections," a Labour source said.

"We've focused relentlessly on the cost of living crisis following 14 years of chaotic Tory failure, and we're fighting for every vote, but winning these seats was always going to be a massive challenge for us." (Reporting by Elizabeth Piper Editing by Ros Russell)