Jeremy Corbyn has refused to say which side he might back in a future Brexit referendum under a Labour government.
He said he would offer voters a choice between Remain and a deal negotiated by Labour, and deliver the outcome.
Pushed on whether he would personally support Leave or Remain, he refused to commit, saying instead: “As PM, my job will be to bring people together.”
His remarks come ahead of Labour’s conference where he is expected to face increasing pressure to back Remain.
According to campaign group Another Europe is Possible, more than 80 motions have been submitted by local Labour groups for debate at conference in Brighton calling for the party to back Remain in a future public vote.
Mr Corbyn’s apparently neutral stance has been openly challenged by First Minister of Wales Mark Drakeford on Wednesday.
He said Welsh Labour “must and will campaign to remain in the EU”.
A number of high profile members of the shadow cabinet, including shadow foreign secretary Emily Thornberry and shadow chancellor John McDonnell, have said they would campaign for Remain.
Labour’s deputy leader Tom Watson has called for another public vote on Brexit before any general election, but Mr Corbyn has said an election should come first.
Mr Corbyn said Labour was the only party offering a choice and he would be asking the Labour conference to “realise the importance of giving the people a choice”.
“I want the people to have a choice between the offer of remaining in the EU and the offer of an agreement with the EU which will give us a trade relationship, which will give us a customs union, will give us rights, consumer rights, workers rights and environmental standards.
“My job, as prime minister, will be to deliver that option that is chosen by the British people.”
Earlier this week, the Liberal Democrats agreed a new manifesto pledge that if they won a majority government in a next election, they would scrap Brexit altogether without another vote.
But their leader, Jo Swinson, said they would continue to call for another referendum alongside other opposition parties until an election was called.
‘Bring people together’
Mr Corbyn initially outlined his position in an interview with the Guardian where he repeated Labour’s four sticking points for a “sensible” deal with the EU – namely a new customs union, a close single market relationship, guarantees of workers’ rights and promises on environmental protections.
Once these were secured, he said they would put that deal to a vote against Remain, adding: “I pledge to carry out whatever the people decide, as a Labour prime minister.”
Mr Corbyn said the pledge made Labour “the only UK-wide party ready to put our trust in the people of Britain”.
Mr Corbyn said Boris Johnson wanted to “crash out” of the EU without a deal, while the new position of the Lib Dems would be a “parliamentary stitch-up” and “simply undemocratic”.
He added: “Labour is the only party determined to bring people together.”
But Michael Chessum, national organiser for Another Europe is Possible, said Labour members were the party’s “the secret weapon” at a general election, and Mr Corbyn “ignores them at its peril”.
“Support for an explicit Remain stance is evidently overwhelming,” he said.
“Only if Labour can get clarity on this part of its policy can it fight the election on its domestic agenda.”
The Conservatives said the growing movement within Labour for the party to campaign for remain showed it wanted to “cancel” the 2016 referendum result.
“They had the chance to let the public decide how to resolve Brexit via a general election – but Jeremy Corbyn doesn’t trust the people,” said party chair James Cleverly.
Meanwhile, the party’s National Executive Committee has voted to scrap its affiliation with Labour Students – which, up until now, had been the official student wing of the party.
Earlier, the chair of Labour’s Momentum campaign group, Jon Lansman, put a motion to the NEC calling for it to set up a new student body.
BBC political correspondent Iain Watson says the motion has now passed, but the group has called the move an attack on party “centrists”.