Labour leader Jeremy Corbyn has called on the next British Prime Minister and Conservative Party leader to hold a second referendum before taking the UK out of the European Union and said Labour will campaign for remain.
Following a meeting of the shadow cabinet at Westminster, Mr Corbyn said that whoever wins the Tory leadership should have the confidence to put any new deal they negotiate with Brussels - or no-deal - to the public.
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 poor showing in the European elections.
In a letter to party members, Mr Corbyn said: "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 Tory leadership race, they will seek to renegotiate the terms of the UK's withdrawal, but would leave without a deal if they failed to do so.
Labour's Brexit spokesman Keir Starmer said that "campaigning for remain ... is a really important point of principle".
In a video posted on Twitter, he said: The trade unions are behind it, the shadow cabinet's behind it, and I know it's what our members want".
Whatever Brexit outcome the new Prime Minister puts forward, we must have another referendum. Remain must be an option and Labour will campaign for remain. pic.twitter.com/gVt2hBbIy5— Keir Starmer (@Keir_Starmer) July 9, 2019