The Shadow Foreign Secretary was put on the spot by BBC host Andrew Marr as he said Labour’s Brexit tests have been designed to make May’s final deal fail in Parliament.
The BBC host pointed out one of the tests says Theresa May’s Brexit deal must guarantee the UK will maintain the same benefits of being a member of the EU outside of the bloc.
A provision which Mr Marr claimed to be impossible to achieve unless the Prime Minister agrees to keep the UK in the customs union and the single market.
He said: “You mentioned your tests a couple of times but they’re a bit silly, aren’t they?
“If you say we must have the exact same benefits then that means that we have to stay inside the single market and the customs union.
“Otherwise we can’t possibly have the exact same benefits.
“So it does seem to a lot of people these are tests designed for the Government to fail them.
“They’re intended to provoke a parliamentary crisis because you want a general election as soon as possible.”
The Labour frontbencher responded arguing Theresa May had already agreed to meet Labour tests on the final agreement with Brussels.
She added Labour will be merely holding the Prime Minister to her promise.
She said: “When Theresa May said she was going to get this deal and we said we will have six tests and she said ‘oh, it’s fine. I’m going to be able to agree on all of that’.
“‘My agreement will meet your test.’ That’s what the Prime Minister said.
“And we’re holding her to it.”
Ms Thornberry hit out at Theresa May’s government for “playing chicken” over the Brexit deal.
She added: “They have been faffing around for two years.
“We shouldn’t be having a deal where Theresa May comes to an agreement that says ‘we haven’t been able to agree anything in the last two years but we’re going to agree something in the next two years.
“It’s a false choice. We’re not agreeing to building half a bridge when we don’t know where it goes.”