Labour will push for a new EU referendum when the Government brings its latest Brexit plans to the Commons in the coming days.
And shadow Brexit secretary Sir Keir Starmer left open the possibility the party could back Boris Johnson's deal if a new national poll was attached to it.
Sir Keir insisted that any agreement approved by Parliament needed to be put to voters in a referendum and the party would back an amendment calling for one.
The Labour heavyweight told BBC1's The Andrew Marr Show: "We need an amendment to say that whatever deal gets through, it should be subject to a referendum.
"We have already voted, I think, three times as a party for a second referendum with a three-line whip behind it.
"The position we have adopted is whatever the outcome, whether it's Boris Johnson's bad deal or a better one which could be secured, it has got to go to a referendum up against remain."