Others will go to the polls in by-elections in Wakefield and Tiverton and Honiton, both triggered after former Tory MPs resigned in disgrace.
The polls are seen as a key test for Boris Johnson’s leadership two weeks after 148 of his own MPs voted in favor of his impeachment in a vote of confidence.
In Wakefield, a former industrial area in West Yorkshire, former Tory MP Imran Ahmad Khan has resigned after being convicted of sexually assaulting a 15-year-old boy and jailed for 18 months.
Wakefield was one of the so-called Red Wall seats won by the Tories in the 2019 general election after having been a Labor stronghold since the 1930s, but Labor is now hoping to take it back.
In Tiverton and Honiton, Devon, Neil Parish, the Tory MP since 2010, resigned after admitting watching pornography on his phone in the House of Commons.
The Liberal Democrats are the main challenger in this rural south-west constituency, where they hope to recreate by-election victories in North Shropshire in December and in Chesham and Amersham a year ago.
Victory for the Lib Dems would require overthrowing a Tory majority of 24,239, but party leader Sir Ed Davey was confident they were ‘neck and neck’ with the Tories on the eve of the vote.
Residents are “fed up with Boris Johnson’s lies and negligence”, he said, as he called on them to support his party’s candidate, former soldier Richard Foord.
“Farmers have been sold off by overseas trade deals, people struggle to access GPs and dentists, and local roads and schools have collapsed.
“Families are facing skyrocketing gas bills and food prices and this government’s only response is to hammer them with constant tax hikes.”
The Prime Minister urged voters to ‘stand up for British food and farming’ by backing Conservative Helen Hurford, a former school headmistress.
In a video shared on social media on Wednesday, Mr Johnson appeared alongside the candidate at a farm, saying the party was working to protect ‘our fantastic food and farming industry and ‘an incredible agricultural sector’.
The loss of the Tory stronghold would be seen as a sign of Mr Johnson’s waning electoral appeal after the party and amid the cost-of-living crisis, and could spark a fresh backlash against his authority.
The Tories face a tougher challenge to retain the Wakefield seat, with Labor now the favorites to overthrow the 2019 Tory majority of 3,358.
Conservative candidate Nadeem Ahmed raised his eyebrows as he said last week that voters should still trust the party after Mr Khan’s sexual assault conviction, just as they still trust GPs despite the crimes of the mass murderer Harold Shipman.
Labor leader Sir Keir Starmer said a victory in the northern constituency “could be the birthplace of the next Labor government”.
On the eve of the opening of the polls, he said: ‘The public is fed up with Boris Johnson and a Tory party that promises big but never delivers.
“Labour candidate Simon Lightwood has campaigned positively – with a plan to bring well-paying jobs and investment to Wakefield, put more police on the streets to tackle anti-social behavior and fight to suppress the unfair rise in national insurance.
“But a vote for anyone other than Labor will let Boris Johnson off the hook. The people of Wakefield have a chance to send a message to the Conservatives that enough is enough”.
If the Conservatives were to lose the two by-elections, it would only be the seventh time that a government had suffered such a double defeat since the Second World War.
Former Lib Dem leader Sir Vince Cable said a loss to the Tories ‘probably doesn’t matter much’ to Mr Johnson’s position as the Prime Minister would say ‘this outcome has been integrated”.
Sir Vince told the PA News Agency: ‘He’s very good at getting away from tight corners.
“I think the real problem for the Conservative government is later this year when the economy gets worse and we have high inflation, a potential recession, a slipping pound, a government budget that is increasingly under pressure.”
Polling stations for the two by-elections will be open from 7:00 a.m. to 10:00 p.m. Thursday, with results expected between 4:00 a.m. and 6:00 a.m. Friday.