Emily Thornberry has told Jeremy Corbyn Labour must decide “now” whether to back Leave or Remain.
Speaking to HuffPost UK’s Paul Waugh at a fringe event at the party’s conference in Brighton, the shadow foreign secretary said members should “thrash it out” this week and not wait until after the election
Stressing Corbyn was a “servant of the members”, Thornberry said: “We’re all here [at conference]. I don’t see why we can’t make the decision now.”
The frontbencher said she feared Labour risked losing 30% of its core vote to Lib Dems and the Greens “unless we are clear about where we stand on Europe”.
It comes as Corbyn attempts to get Labour members to back a Brexit “compromise” which would see the party only declaring a position when a second referendum was called or in a post-general election special conference on Brexit.
Thornberry added: “I think that this conference should thrash it out.”
Likening the squeeze on the Labour vote to a Star Wars scene in which the characters are almost crushed between two walls, she said: “We can’t just stand there and say ‘I’m right’.”
Corbyn risks being repeatedly asked about Brexit by journalists and the public during the campaign if he failed to back one side, she added.
She said: “My concern, obviously, is that the next general election could be a Brexit election and just be about one issue.
“And we have to be very careful that it doesn’t come to that, but it does seem to me that one way in which we will be able to help ourselves is by having a clear line on Brexit, so that we can also talk about everything else, so that when Jeremy goes onto television he’s not constantly asked, what’s your policy on Brexit.”
London Mayor Sadiq Khan has also intervened to urge Labour delegates to refuse support for “any compromise on Brexit” and to force Corbyn to whip his MPs in favour of backing Remain.
He added in a Facebook post appealing to members: “Do not accept a fudge, do not delay us setting out what our stance would be in any future referendum.”
He said: “Labour has come to a crossroads. At conference this week, we have the opportunity to come together to define how we seek to deal with the biggest challenge facing our country - Brexit.”
His statement goes on: “Labour is a Remain party and we need to make this official by making it our policy to campaign to stay in the European Union under all circumstances - and to whip our MPs to back that position.
“Staying neutral in the face of the biggest economic and social threat to our country for decades is simply not an option.
“It’s time for Labour to commit to stopping Brexit - not only by promising to give the British public the final say, but by pledging to throw all our energy behind the campaign to stay in the European Union.”