U.K. Shadow Foreign Secretary Emily Thornberry | Leon Neal/Getty Images Emily Thornberry: Labour could vote for vague Brexit deal The shadow foreign secretary said that Labour MPs might be forced to back an eventual withdrawal agreement if it was non-specific.

LONDON — The U.K.'s opposition Labour party could back Theresa May's Brexit deal in parliament becuase the terms of the future relationship with the EU are likely to be too vague to object to, the party's foreign affairs spokesperson said.

Emily Thornberry, the shadow foreign secretary, predicted that the exit deal secured by the government would be a "blah, blah, blah divorce" that left key decisions about the U.K.'s future relationship with the EU undecided.

Labour has set six tests that the government's Brexit deal must meet before the party backs it. But Thornberry, speaking during an event at the Chatham House think tank on Wednesday, said that "if you hold up 'blah, blah, blah' to six tests, you probably pass it."

Support from Labour for a deal would all but guarantee that it passes when MPs vote on it in the autumn, clearing the way for the U.K.'s exit on March 29 2019. Anti-Brexit campaigners have pinned their hopes on MPs rejecting the deal, leading to further negotiations or another referendum.

However, senior Labour officials played down the significance of Thornberry's comments.

"We have always been clear that the tests are what we will judge the final deal on, and how we will take a voting decision. That decision will be taken in October," one official said.

During the event, Thornberry said she expected the substance of the negotiation with the EU on the future relationship to take place during the immediate post-Brexit transition period.

“If past evidence, of the last few months is anything to go on, it’s going to be a 'blah, blah, blah' divorce, it’s not going to actually make any decisions, it’s going to continue to kick things down the road," she said.

Referring to the expected autumn parliamentary vote, she added: "What is it that we’re going to be agreeing on? We have our six tests, if you hold up ‘blah, blah, blah’ to six tests, you probably pass it. And then we leave the EU and then we’re in the status quo ... and during that period there has to be a negotiation for what our final relationship will be. I just hope upon hope that we have a general election in the meantime and frankly that the grown-ups turn up and we’re able to do the negotiation. But who knows."