Labour will back a second referendum when Boris Johnson brings his Brexit plans to the Commons next week.
Speaking on Sunday, shadow Brexit secretary Sir Keir Starmer left open the possibility the party could back Boris Johnson's deal if a new referendum 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."
He added: "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."
Asked if Labour could back the Government's deal if it came with the pledge of a new referendum, Sir Keir said: "Well, we'll see what that looks like.
"What we are trying to achieve is that this deal in particular, but any deal, is put up against Remain in a referendum. And we will have to see tactically how we get there."
However, Labour leader Jeremy Corbyn may not table the amendment himself to avoid "alienating" pro-Remain parties, shadow chancellor John McDonnell said.
Speaking to Sophy Ridge on Sky News, he added: "We've always said, if Boris Johnson is confident about this deal, go back to the people with it.
"We voted for the Kyle-Wilson amendment before which called for a second referendum.
"Tactically, these things are often better moved from the back benches where you can secure cross-party support and where you're not alienating people purely and simply because it's the leader of the opposition moving it.
"What we've said is Boris Johnson should take this deal back to the people."
