Frank Field has said he will not trigger a by-election after resigning the Labour whip over the anti-Semitism row and allegations of bullying in the party.
The veteran MP had faced calls to seek a vote in his Birkenhead seat after saying there had been an “erosion of our core values” under Jeremy Corbyn and announcing he would sit as an independent.
Labour sources said resigning the whip meant he had “automatically opted to resign” from the party and should stand again for the seat.
But Mr Field, who represented the seat for Labour for almost 40 years, said on Monday he had received wide support from people in his constituency, who “stressed I should simply get on with the job of representing Birkenhead”.
Mr Corbyn had earlier said that he did not “see why he had to resign” the Labour whip.
The combative MP said: “I now have what may become a major legal dispute with the Labour Party over my continuing membership of the party.
“I shall fight any attempt at expelling me in every way I can and, if need be, in the courts.
“This interpretation of Labour’s rulebook could last a long time.”
Mr Field quit the parliamentary party on Thursday, citing “a culture of intolerance, nastiness and intimidation” among local members.
The Labour leader said on Monday he was “sorry” about the decision and that there was no place for bullying.
But he also insisted that there had to be “democratic debate within the party”.
Speaking in nearby Liverpool on Monday as he prepared to travel across the north of England campaigning on transport issues, Mr Corbyn said: “I’m sorry he’s resigned and I thank him for all the work that he’s done as an MP and for the party, but I don’t see why he had to resign.”
Asked about Mr Field’s claims of bullying in the party, the Labour leader said he did not know what the claims were, adding: “I invite all MPs to take part in the discussion and the debate.
“Obviously bullying and intimidation have no place whatsoever in any political party, particularly the Labour Party, but there has to be democratic debate within the party.”
Mr Corbyn also became animated and said “can I finish my answer” as a reporter tried to interrupt him during the interview.
He also seemed to back a proposal by the grassroots Momentum group to create an “open, inclusive selection process” for MPs.
Asked by ITV whether the plan – which critics suggest is a cover to deselect Mr Corbyn’s opponents – was a good idea, he said: “We are a party whose membership has grown to half a million from less than 200,000 three years ago and clearly there have to be some changes and more democratic accountability of everyone within the party and I’m happy there should be greater democratic accountability.”
Labour’s crisis over accusations of anti-Semitism is reaching a showdown moment as senior figures demand the leadership take firm action to prove the party is not hostile to the Jewish community.
Ahead of a crunch meeting of the ruling National Executive Committee on Tuesday, leading MPs have insisted the party must finally adopt the definition of anti-Semitism set out by the International Holocaust Remembrance Alliance (IHRA) in full.
The calls came after the issue continued to rock the party, with former minister Dame Margaret Hodge standing by her claim that Mr Corbyn was an “anti-Semitic racist”.
Dame Margaret said she believed her view was confirmed by reports in the media in recent weeks after a video emerged of Mr Corbyn stating that British Zionists “don’t understand English irony” at a conference in 2013.
Former prime minister Gordon Brown also insisted on Sunday that the IHRA definition must be adopted.