And it could become again the trigger for a new row over Britain's divorce from the European Union, with a move by the leadership to accept a motion for a second referendum failing to close the divisions that have long dogged the Labour Party.
Mr Corbyn has been reluctant to support a second referendum, but said on Sunday he would abide by the decision taken by activists at the party conference today.
"We weren't ruling out options and nobody was ruling out Remain".
Speaking to the BBC's Andrew Marr as the party faithful gathered in Liverpool, Corbyn said he would be "bound by the democracy of our party" were members to vote in favour of a second referendum, although he added he would wait and see what wording would be put in front of the delegates after a meeting on Sunday evening.
"No "ifs", no "buts", Starmer will say in a speech to the party's annual conference, according to advance extracts.
"All the polling that we have seen is that the country is still pretty split down the middle".
Members at the conference will vote on a motion set before them on Tuesday (25 September).
He claimed most Labour Party members and members of Mr McCluskey's union wanted the option of staying in the EU.
My understanding of what the discussion, certainly within my party has been all about, is: respect the referendum but the deal that comes back, if it's not acceptable to Parliament, we should have a general election or keep the option of a People's Vote on the deal on the table.
Last night Sir Keir said: 'If Theresa May brings back a deal that fails our tests - and that looks increasingly likely - Labour will vote against it.
A People's Vote campaign spokesman said the conference motion was "clear movement" towards adopting a referendum.
It is an argument Labour's leadership feels keenly, and one that nearly certainly chimes with Corbyn, a veteran eurosceptic who in 1975 voted "No" to Britain's membership of the then-European Community.
"In that case it will be about whether you accept the deal or not or whether you send people back to negotiate a proper deal".
But some Tory moderates had hoped that, faced with the prospect of no deal, some Labour MPs would vote with the Government.
"They did not do this to be offered a farcical referendum on No Deal or a Bad Deal".
"And if the prime minister thinks we'll wave through a vague deal asking us to jump blindfolded into the unknown she can think again".
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