Labour's shadow Brexit secretary Sir Keir Starmer has insisted "nobody is ruling out Remain as an option" in a fresh referendum on the UK's relationship with the EU.
In a bid to push past confusion on Labour's position should there be a second public vote, Sir Keir declared the party could still back voters having the choice of staying in the EU.
In his speech to Labour's conference in Liverpool, Sir Keir said if Theresa May could not reach a Brexit deal with the EU, or parliament votes against an agreement, then Labour "must step up again and shape the debate".
He said: "Our preference is clear, we want a general election to sweep away this failed government."
And, deviating from a draft version of his speech, Sir Keir added: "But, if that's not possible, we must have other options. That must include campaigning for a public vote.
"It's right that parliament has the first say, but if we need to break the impasse our options must include campaigning for a public vote and nobody is ruling out Remain as an option."
Sir Keir's declaration brought a standing ovation from many delegates in the conference hall and the biggest cheer of his entire speech.
However, veteran Labour MP Dennis Skinner, who backed Leave, notably did not applaud while a top union leader immediately contradicted Sir Keir's message.
Sir Keir's words will be viewed as a rebuke to shadow chancellor John McDonnell, who told Sky News on Monday a fresh referendum should be "on the deal itself" and not another choice between Leave or Remain.
Sparking claims of a split at the top of the party, Sir Keir later contradicted Mr McDonnell's stance, prompting him to row back and admit Sir Keir was correct to say Labour was "keeping all the options on the table".
6:01The Conservatives seized on Sir Keir's conference address, with Tory party chairman Brandon Lewis accusing Labour of wanting to "take us back to square one on Brexit".
Sir Keir also faced accusations of a "betrayal" of Labour voters by the party's Brexiteers, as well as claims he used his speech to position himself as a potential replacement for Jeremy Corbyn.
Brendan Chilton, the general secretary of Labour Leave, said: "Keir's speech today was a challenge to Jeremy's leadership.
"It was a carefully calculated pitch, no doubt written with a team of advisers. He is undermining Jeremy, John McDonnell and millions of Labour voters – and he knows it.
"At times the speech had more in common with a leadership stump speech than a policy announcement.
"Many people will wonder whether Sir Keir is trying to line himself up as the Remain replacement for Jeremy."
Later on Tuesday, Labour members will vote on whether to back a motion committing the party to keeping "all options remaining on the table" – including a second referendum – should parliament vote against the prime minister's Brexit deal and a general election not follow.
Speaking during a conference debate on the motion, Steve Turner, assistant general secretary of Unite the union, told delegates if the government loses a parliamentary vote on the Brexit deal and fails to grant a general election, then "we demand they go back to the people with a vote on the deal".
However, he added: "That is not a second referendum. Despite what Keir may have said earlier, it's a public vote on the terms of our departure.
"We desperately need a better, fairer society. We need to heal the wounds of Brexit not reopen them.
"And only our movement, united with a proud socialist Labour government, is capable of doing that."
Sir Keir told the conference that Labour MPs would vote against a Brexit deal if the government's agreement with the EU fails to meet his party's six tests.
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At a fringe event prior to Sir Keir's conference speech, former Europe minister Caroline Flint MP attacked her party's six tests as "pretty vague and impossible to quantify".
She added: "A new referendum will divide voters again, it will tell Labour voters if they voted Brexit they may as well vote Tory. And that cannot be allowed to happen."
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