Labour is to press the next Tory leader to hold a second referendum before taking Britain out of the EU – with a commitment that the party would campaign for Remain.
The decision by the shadow cabinet was broadly welcomed by pro-Remain MPs, who have been pressing the party to fully embrace a second referendum.
However, the meeting left open what position the party would take if the new prime minister were to call a snap general election.
The move follows weeks of wrangling within the party over its position on Brexit – backing a second referendum only in certain specific circumstances – which was widely blamed for its dismal showing in the European elections.
It comes after the leadership broadly secured the backing of the main trade union bosses – including Unite general secretary Len McCluskey, who had been holding out against a second referendum.
Announcing the move in a letter to party members, Jeremy Corbyn said: “Whoever becomes the new prime minister should have the confidence to put their deal, or no-deal, back to the people in a public vote.
“In those circumstances, I want to make it clear that Labour would campaign for Remain against either no-deal or a Tory deal that does not protect the economy and jobs.”
Deputy leader Tom Watson, who has been at the forefront of demands for the party to back a second referendum, welcomed the decision.
“Our members have been telling us for some time now they want us to be a Remain party, they want us to put the new deal to the people,” he told the BBC.
“We are now going to campaign for that. I am very proud the shadow cabinet have listened to their concerns.”
Shadow Brexit secretary Sir Keir Starmer said he was “really pleased” with the commitment, describing the campaign for Remain as “a really important point of principle”.
However the chairman of the Commons Brexit Committee, Hilary Benn, warned the party would have to make clear what it would do in the event of a general election.
“If Labour goes into that election saying we’re going to try and deliver Brexit then I think we’d find it very, very hard indeed to win that general election,” he told BBC Radio 4’s The World at One.
However there was dismay among pro-Brexit Labour MPs who warned the decision would play into the hands of the Tory leadership frontrunner Boris Johnson.
John Mann, the MP for Bassetlaw, said there was no sign that voters in the party’s traditional heartlands in the North and Midlands who backed Leave in the referendum, had changed their minds.
“The one person who will be smiling at today’s announcement is Boris Johnson,” he said.
“I think it makes it slightly more likely that he’ll be tempted to call a Brexit election. Labour will lose votes of those Labour voters who voted Leave.”
Mr Corbyn, who had been resisting demands to adopt a more pro-Remain stance, said that he had wanted to bring the party with him before shifting its position.
“What I’ve done is what I think a leader should do and that is spend some time listening to people,” he told BBC News.
“Many of my colleagues have found this a very frustrating experience because they’ve said ‘Why don’t you just tell us what to think?’
“No, I want to take the movement with me.”
He acknowledged, however, that the party would have to move swiftly if the new prime minster did decide to call an election.
“We have a democratic process, we will decide very quickly at the start of that campaign exactly what our position will be,” he said.
The Liberal Democrat Brexit spokesman Tom Brake said: “Jeremy Corbyn can pretend all he likes that the Labour Party are finally moving towards backing the Liberal Democrat policy of a People’s Vote.
“But it is clear it is still his intention to negotiate a damaging Brexit deal if he gets the keys to Number 10.”