The Labour Party will vote against a Brexit deal agreed with European Union nations unless it is guaranteed that the UK will have exactly the same economic and trading relationship with the bloc that Britain currently enjoys.
Deploying the same language used by Brexit Secretary David Davis when questioned by fellow MPs, his Labour counterpart Sir Keir Starmer said any deal Prime Minister Theresa May agrees must ensure that Britain has the "exact same benefits" after Brexit.
Starmer is set to lay out Labour's demands for any deal at a speech at Chatham House on Monday (27 March) where he will say the deal must meet six key tests.
He will argue that Britain must have an arrangement where it benefits from the European single market and customs union, among others, or Labour would not side with the government.
Labour has repeatedly said it would not obstruct the "will of the people" with its desire to leave the European Union, but it will hold May to account after Article 50 is triggered.
Appearing on the BBC's The Andrew Marr Show on Sunday (26 March), Starmer said: "What I'm setting out tomorrow is six tests for the final deal for Brexit.
"So far, all the attention has been on should the prime minister have permission to start the negotiations. We're through that part. Now, what comes into focus is, 'What is the right deal?' because this is about our future relationship with the EU."
He added: "If our tests are not met then we do not intend to support the deal the government comes back with."
When questioned about the slim likelihood such a prospect is secured, Starmer said: "We're not inside [the single market], I accept that. I do not accept that we can't have the same benefits.
"Those words, 'exact same benefits' are not my words. They're in my test but they are taken from David Davis, the secretary of state for exiting the EU. When he was pressed on this in parliament, he said that he would deliver a comprehensive free-trade agreement and a customs arrangement that delivered the exact same benefits as the single market and the customs union.
"So we're holding him to that test. The government can't turn around now and say this is unachievable because it was David Davis, who the prime minister has appointed in the role of exiting the EU, who set that as his [inaudible]."
Labour leader Jeremy Corbyn has reportedly supported Starmer's proposition to vote against the Brexit deal if certain arrangements are not agreed in an interview with the Independent.
The warning comes from Labour days before May is set to announce the Great Repeal Bill and trigger Article 50 on Wednesday (29 March).