Jeremy Corbyn has called on the next prime minister to hold a second referendum on Brexit, and has committed Labour to backing Remain.
The Labour leader said whoever wins the Conservative leadership contest should have the confidence to put any new deal they negotiate with Brussels – or no-deal – to the public.
It follows months of wrangling within the party over its position on Brexit, with Labour previously backing a fresh EU vote only in certain circumstances.
In a letter to party members, Corbyn said Labour would campaign for Remain “against either no-deal or a Tory deal”, but did not explain what Labour would do if it won a general election.
The move comes a day after leaders of some of the party’s largest affiliated trade unions moved to back a second referendum.
Among those present was Unite general secretary Len McCluskey, a key ally of Mr Corbyn, who has previously resisted calls for a confirmatory vote.
Corbyn wrote in his letter: “Now both Tory leadership candidates are threatening a no-deal Brexit – or at best a race to the bottom and a sweetheart deal with Donald Trump.
“I have spent the past few weeks consulting with the shadow cabinet, MPs, affiliated unions and the NEC (national executive committee). I have also had feedback from members via the National Policy Forum consultation on Brexit.
“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.”
Both Boris Johnson and Jeremy Hunt have said that, if they win the race for No 10, they would seek to renegotiate the terms of Britain’s withdrawal, but would leave without a deal if they failed to do so.
Hunt accused the Labour leader of having “never believed in Britain”, adding: “In this country we deliver on the will of the people. We will deliver Brexit and make a success of it.”