Despite intense pressure from his own MPs and members, Jeremy Corbyn has seen off an attempt to commit the party to a confirmatory referendum on any Brexit deal.
The proposal was defeated in a marathon meeting of the party's ruling National Executive Committee (NEC) to finalise the Labour manifesto for the upcoming European elections.
Labour will instead stick to the wording of a motion passed by the party conference last year, which keeps a public vote on the table - but only as a final option.
A party source made clear that this committed Labour to back a fresh vote only if the party cannot either win the changes it wants to Theresa May's Withdrawal Agreement or secure a general election.
Deputy leader Tom Watson, who has led calls for a more positive stance on a second referendum, left the six-hour meeting without comment, saying only that the manifesto would be published early next week.
Mr Watson had earlier walked out of a shadow cabinet meeting after being told it would not be shown the proposed wording of the manifesto commitment.
Some 115 MPs and MEPs signed a letter to NEC members organised by the Love Socialism, Hate Brexit group urging them to explicitly back a referendum in the manifesto.
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The change was backed by a number of major unions, including the GMB, Unison and Usdaw.
And 34 of Labour's 70 candidates in the May 23 European elections have pledged to campaign for a referendum and then back Remain if a vote is called.
A Labour source said: "The NEC agreed the manifesto which will be fully in line with Labour's existing policy - to support Labour's alternative plan, and if we can't get the necessary changes to the Government's deal, or a general election, to back the option of a public vote.”
Following the meeting, Mr Corbyn left party HQ by a back entrance and was seen being driven away in a people carrier.
His car was momentarily blocked by pro-Remain protesters.
The founder of the Corbyn-backing Momentum movement Jon Lansman said only: "Good meeting.”
Sources from inside the room characterised the meeting of the 41-member NEC, which brings together representatives of the party leadership, MPs and members as well as unions, as "respectful, constructive and comradely throughout”.
And Mr Watson insisted there was "no rancour at all" in his walkout from the earlier shadow cabinet meeting, saying: "I politely asked if the shadow cabinet were going to see the draft words and was told 'no'. So I left to walk to the NEC.”
A Labour spokesman said that the European election manifesto would be published “soon".
"Labour is the only party which represents both people who supported Leave and Remain," said the spokesman.
"We are working to bring the country together after the chaos and crisis created by the Tories.”
However, Chuka Umunna, spokesman for pro-Remain party Change UK, accused his former party of "prevarication" over a referendum.
At the first in a series of Change UK rallies, he urged Labour supporters to "lend us your vote in these European elections”.
"The better we do, the more likely you are to see the Labour leadership adopt a People's Vote and Remain position," Mr Umunna told the rally in London.
Labour MP Jess Phillips warned the party would face a "drubbing" if it went into the European elections without a clear promise on a second referendum.
And Corbyn-backing Labour MP Lloyd Russell-Moyle warned that a failure to offer a referendum could scotch the party leader's chances of getting to 10 Downing Street.
"Only way JC will be PM is to offer a confirmatory vote - we could be out of power for a generation and the left will be swept away in Labour," tweeted the Brighton Kemptown MP.
"This is the fight for the left project and many are committing self harm.”
Recent polling shows Labour lagging behind Nigel Farage’s Brexit Party - who have topped a rolling average of EU voting intention.