Jeremy Corbyn could announce Labour’s backing for a second referendum within days after the party suffered huge losses in the European elections.
The leader has been under pressure to get behind a people’s vote after Labour lost 10 MEPs on Thursday.
Labour’s preference is for a general election but many MPs and members have been pushing for support for a second referendum.
A senior Shadow Cabinet minister told the Daily Mirror: “We need to be more definitive quickly and you’ll see that in the next couple of days, to give our membership confidence again that they can get back on the doorstep, because they couldn’t this time round.”
Mr Corbyn said on Monday that any Brexit deal must be put to a public vote after sustained criticism that the party’s attempt to appeal to both remain and leave backing members had failed.
Shadow Foreign Secretary Emily Thornberry said Labour should call for a second referendum and Shadow Chancellor John McDonnell said going back to the people was now the “only option”.
Shadow Home Secretary Diane Abbott added: “We’re supporting a people’s vote strongly now because it’s the right thing to do and it’s democratic.
“There is no inherent contradiction between respecting the result of the referendum and having a people’s vote, not least because it’s still not sure how a people’s vote would pan out.”
Labour came third in the European elections, with ten seats and 14 per cent of the vote – a drop of 11 per cent and halving their number of MEPs.
Former Prime Minister Tony Blair urged Labour to set out its position on Europe if it ever hoped to win an election.
He said Mr Corbyn had to come to a “clear position” on the EU, adding: “Both parties have made the same mistake of sitting on the fence on Europe and thinking you can appeal to both sides.
“What the European elections show you is that isn't possible."
Mr Blair also said he voted Labour “without any great enthusiasm” and believes the party should “stop equivocating” on Brexit.
He added that he thought it was “more likely” the country will vote to stay in the EU if there is another referendum, but it is an “era of unpredictability”.
His comments come as Shadow Home Secretary Diane Abbott said Labour was moving towards a “clearer line” on Brexit.
The MP for Hackney North and Stoke Newington said there was "no inherent contradiction" between respecting the result of the 2016 referendum and having another poll, as calls for the party to fully throw its weight behind a so-called People's Vote intensified.
Labour deputy Tom Watson and shadow Brexit secretary Sir Keir Starmer have both also called for a shift in stance to back a second referendum over Mr Corbyn's preference for a general election.
