- Video report by ITV News political correspondent Carl Dinnen
Michel Barnier has cast doubt on Theresa May's proposals for post-Brexit customs arrangements in his first public response to last week's White Paper.
The EU Chief Negotiator for Brexit said the White Paper had opened the way for "constructive discussions" on the relationship between the EU and the UK, but the plans must be "workable."
He said there were elements of the plan agreed by the Cabinet earlier this month at Chequers which the European Commission did not understand, and said further discussions would be needed over the coming weeks to establish how much "common ground" exists between London and Brussels.
Mrs May has urged the EU to change its Brexit negotiating position, arguing that some previous proposals have been "unworkable".
Mr Barnier stated the priority was to protect the EU's single market and that the White Paper proposals, which would allow trade in goods but not services, could put that at risk.
"We are not going to negotiate on the basis of the White Paper because that's the British paper but we could use many elements of the White Paper."
"There's not an awful lot of justification for the EU running the risk of weakening the single market.
"That is our main asset. There's no justification for us to create additional burdens on business just because the UK wants to leave," he said.
The prime minister has already experienced extreme fall-out within her own party following the release of the White Paper.
Speaking in Belfast for her first major Brexit speech since the wave of major Cabinet resignations, Mrs May described the white paper proposals as “a significant development of our position … a coherent package”.
“It is now for the EU to respond – not simply to fall back on to previous positions which have already been proven unworkable, but to evolve their position in kind.
“And, on that basis, I look forward to resuming constructive discussions," she said.
The proposals aim to tie up loose ends by autumn in an attempt to reach an arrangement on a post-Brexit relationship that will avoid the UK leaving the EU with no deal.
Mr Barnier did indicate the EU was prepared to amend its "backstop" proposals for the Irish border, which has become a large area of contention in talks.
Mrs May reiterated her opposition to the EU backstop, which would essentially allow Northern Ireland to remain in the single market and the customs union, saying the idea was “something I will never accept and I believe no British prime minister could ever accept”.
Equally, she said that a hard border between Northern Ireland and the Republic was “almost inconceivable”.
Twenty years after the Good Friday Agreement, the return of any form of physical checkpoints or other infrastructure would be “an alien concept”.
Mrs May said that her White Paper proposals, which would see the UK remain within the single market for goods and adopt a “common rule book” of regulations with the EU, was a “credible third option” that would “honour the Belfast Agreement, deliver on the referendum result and be good for our economy”.
Mr Barnier argued that the EU had a responsibility "to be prepared for all scenarios, including no deal".
His retort added that the European Union had been "creative and flexible" regarding the backstop, and added that the issue needed to be "de-dramatised".
The prime minister also lashed out at internal Conservative critics of her plans for the Irish border, accusing them of being ready to “betray” the people of Northern Ireland and the Republic.
Mrs May also took a swipe at former foreign secretary Boris Johnson’s claim – repeated in his resignation speech to the Commons on Wednesday – that technological solutions could be used to avoid the need for infrastructure at the border.
“No technology solution to address these issues has been designed yet or implemented anywhere in the world, let alone in such a unique and highly sensitive context as the Northern Ireland border,” she said.