Labour risks being crushed like a film hero stuck between walls closing in on each other, if it does not make clear where it stands on Brexit, the party’s shadow foreign secretary has warned.

Emily Thornberry also said the party could lose 30% of its vote share to the Greens and Liberal Democrats, if it is not clear on its position on Europe.

The pro-Remain MP told a HuffPost fringe event at the Labour Party conference in Brighton that Remain voters’ positions on Brexit were their first priority when it comes to voting in an election.

She said: “Clearly the polling is there and does make the case that we are likely to lose many, many more people who voted Remain in the referendum than people who voted to Leave.

“The reasoning seems to be this: that amongst Leave voters on the whole there are a whole panoply of things which they need and they cannot get from any other government than a Labour government.

“So they are aligned with us on all the things that matter to them on a day-to-day basis, and yes, we disagree with them on Brexit, but when it comes to Remain the Remain voters tend to have it as their first priority.

“And the polling does show that we could lose 30% of the Labour vote to the Greens and the Lib Dems unless we are clear about where we stand on Europe.”

Ms Thornberry warned that if the party did not make up its mind it risks being crushed as if it was inside the Star Wars trash compactor, or the closing walls in Indiana Jones.

She said: “I’ve been thinking about this quite a lot and I keep running through lots of films. You get the hero who is standing in the middle and the walls are coming in.

“It is used lots of times, it’s used by Indiana Jones where there are walls coming in, or Zorro, and I think there’s also a bit in Star Wars where they’re in the crusher.

“And the answer is not to just stand there and go ‘oh well, I know I’m right’ – the idea is to get out of there and that’s kind of where we are with these two sides pushing us.”

She also said she did not support Labour holding a “special conference” to decide the party’s Brexit position.

“I don’t see why we can’t make a decision now,” she said.