Shadow Brexit secretary Sir Keir Starmer has ramped up the pressure for Labour to move towards backing a second referendum.
The frontbencher argued the point had been reached where Labour had agreed that if a general election could not be secured then the party “must” consider all options on the table, including a further public vote.
Stressing the importance of the previously made commitment, he insisted it was “one we must keep”.
His stance is in contrast to that of party leader Jeremy Corbyn, who has resisted calls for a second vote, amid concerns of a backlash from Labour voters who supported Brexit.
Having secured the crushing defeat of Theresa May’s EU withdrawal deal, Labour had moved to trigger a general election through a vote of no confidence but the prime minister had “clung on”, Sir Keir told the Fabian Society new year conference in London.
Although this was the “beginning not the end” of the push to force a poll, he argued Labour had now reached the “third phase” of its agreed party policy.
This was the pledge made at the party conference last year in Liverpool that if it was unable to force a general election all options must remain on the table, including campaigning for a public vote.
Drawing cheers, he said: “That was our commitment. It’s a very important commitment.
“It was a commitment to our members, our movement and one we must keep.
“As I set out in Liverpool, a public vote has to be an option for Labour. After all, deeply embedded in our values are internationalism, collaboration and cooperation with our European partners.”
Sir Keir again made clear he believed that in the event of a second referendum, the option of remaining in the EU must be on the ballot paper.
“I don’t think it is any secret I firmly believe there should be a Remain option – and there has to be a genuine Leave option,” he said.
He said that with the raft of legislation that is still needed to get through parliament before Brexit, it was difficult to see how an extension to Article 50 could be avoided.
Article 50 is the legal process by which the UK would quit the EU and the leaving date is scheduled for 29 March this year.
Sir Keir said: “It seems inevitable to me that the government will have to apply for an extension of Article 50.
“So, it’s time for us to inject some honesty into this debate, and to identify the credible solutions that remain.
“In the coming weeks parliament will have the chance to take control. That starts by being open about the dilemmas we face, and the credible choices that are still available.”
The prime minister is spending the weekend at her official country retreat at Chequers working on a statement to MPs on Monday setting out her approach following the overwhelming rejection of her Brexit deal by MPs.
Meanwhile, former prime minister Sir John Major has called for a free vote for MPs aimed at ending the parliamentary stalemate.
He told the BBC there needed to be a series of “indicative” votes to establish which, if any, of the various alternative proposals could secure majority support in the Commons.
:: Sky News will broadcast a special live debate called Brexit Crisis – Deal Or No Deal tomorrow evening from 7pm to 8pm.
An invited audience of voters in the divided city of Leeds will react to the results of a Sky data poll on some of the key issues facing the country.
(c) Sky News 2019: Starmer shifts Labour towards second EU referendum