Labour leader Jeremy Corbyn is facing a growing rebellion against his stance on Brexit.
Party whip Jeff Smith has said he will go against Mr Corbyn’s orders to allow Theresa May to start the Brexit process.
The move follows shadow transport minister Daniel Zeichner - whose Cambridge constituency voted for Remain in the referendum - saying he would defy his party leader because it was a “very straightforward decision” for him to take.
“It’s my strongly held personal position, and I represent three-quarters of the people of Cambridge,” he told the Cambridge News.
“I’ve had perfectly civilised conversations (with the Labour leadership). They know my position and they understand exactly why I’m doing what I’m doing and it’s for them to decide what to do next.”
His announcement came after Tulip Siddiq resigned as a shadow education minister, saying she would be better able to fight against a “hard Brexit” from the backbenches.
The latest moves followed Mr Corbyn’s decision to imposed a three-line whip on Labour MPs, requiring them to back the Bill allowing the Prime Minister to trigger Article 50 and begin the two-year countdown to Brexit.
Shadow home secretary Diane Abbott defended Mr Corbyn’s stand.
She told the BBC Radio 4 Today programme: “You have to remember how this looks to people in post-industrial Britain, former mining areas, the North, the Midlands, South Wales - it would look as if elites were refusing to listen to them.
“It would be wrong. How could MPs vote for a referendum and then turn around and say ‘It went the wrong way so we are ignoring it’?”
Mr Corbyn said he understood the “pressures” facing his MPs, many of whom strongly supported the Remain cause, but urged the party to unite and make sure the legislation goes through the Commons.
Mr Corbyn said: “Labour is in the almost unique position of having MPs representing constituencies in both directions, and very strongly in both directions.
“I say to everyone, unite around the important issues of jobs, security, economy, rights, justice, those issues, and we will frame that relationship with Europe in the future outside the EU, but in concert with friends, whether those countries are outside or inside the EU.”
However Ms Siddiq, whose Hampstead and Kilburn constituency in north London also voted strongly for Remain, said she had to represent the views of her north London constituents, who voted overwhelmingly to Remain.
“I have always been clear - I do not represent Westminster in Hampstead and Kilburn, I represent Hampstead and Kilburn in Westminster,” she said in her resignation letter.
Earlier, there was better news for Mr Corbyn as shadow business secretary Clive Lewis - who has previously said the Prime Minister’s plans for Brexit were not in the best interests of his constituents or the country - said he would toe the party line.
“I have been clear throughout that I respect the result of the referendum and will, therefore, join my colleagues in voting for the Bill on its second reading,” he said.
“However, Theresa May does not have a mandate to dictate the terms of Brexit without listening to the British people.”