Mike Hill has quit as an MP, Labour has confirmed, triggering a by-election.

The sudden announcement sets up a fresh electoral contest in Hartlepool, a seat long-held by Labour, marking the first test of Sir Keir Starmer’s leadership since taking over from Jeremy Corbyn last year.

“Mike Hill has resigned as Member of Parliament for Hartlepool with immediate effect,” a party spokeswoman said.

On Tuesday, Mr Hill appeared to have deleted his Twitter account.

The 57-year-old had represented the North East of England town since 2017.

He held off a Conservative and Brexit Party challenge at the last election but saw his majority slashed by more than half to just under 3,600.

His resignation follows reports that he used taxpayers’ money to fight a staff member’s claim of unfair dismissal, sexual assault and harassment.

Mr Hill was suspended by Labour in September 2019 over allegations he sexually harassed a woman, but had the whip restored to contest the general election two months later.

According to the Sunday Times, Mr Hill claimed £2,000 on parliamentary expenses for the excess on his employment liability policy as he looked to fight the allegations.

The newspaper said he had failed to keep his name secret in the legal proceedings.

Bookmaker Coral has made the Tories odds-on favourites to win the by-election at 1-2, with Labour at 13-8 to retain the seat that was once held by Lord Peter Mandelson, a former cabinet minister and one of the architects of New Labour.

The bookies’ spokesman John Hill said: “Labour have won every election in Hartlepool since this seat was first contested in 1974, however, our betting suggests the Conservatives could break that stronghold in this by-election in what would be a huge blow for Keir Starmer.”

The forthcoming Hartlepool vote to elect a new MP will bring to an end the longest wait for a by-election on record.

On March 5, a total of 582 days passed since voters last went to the polls in a Westminster by-election – a gap that is unprecedented in post-war history, according to analysis by the PA news agency.

The previous record was 581 days, which was the period of time between the Ogmore by-election on February 14 2002 and the Brent East by-election on September 18 2003.

Senior Labour figure Anneliese Dodds did not comment on Mr Hill’s resignation when asked about it during a virtual event with the Reform think tank, instead focusing on the upcoming local elections in May.

“We have a whole range of elections coming up very, very soon,” the shadow chancellor told the event.

“We have local elections and they don’t necessarily hit the headlines as much, but for their impacts on people’s living standards, they are absolutely critical.”