The EU’s chief Brexit negotiator has questioned whether Theresa May’s proposals for customs arrangements are workable, in his first public response to last week’s white paper.

Speaking after briefing ministers from the 27 remaining EU states in Brussels, Michel Barnier said the white paper has opened the way for “constructive discussions” on the post-Brexit relationship between the EU and the UK.

And he indicated the EU was ready to amend its “backstop” proposals for the Irish border, which have become the biggest stumbling block in talks.

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’s proposal for a “facilitated customs arrangement” opened up the risk of major fraud, additional bureaucracy and damage to EU businesses, he said.

Tory arch-Eurosceptic Jacob Rees-Mogg said Mr Barnier’s “aggressive” comments “show why we are right to be leaving the mafia-like European Union”.

Mr Barnier was speaking shortly after Mrs May issued a challenge to Brussels to “evolve” its negotiating position in response to the publication of her Brexit blueprint.

Theresa May
Prime Minister Theresa May urged the EU to ‘evolve’ its position on Brexit (Charles McQuillan/PA)

He said the EU had always been “creative and flexible” in its approach to negotiations.

But he insisted that future talks would be based on the guidelines issued by the European Council in March – which included the controversial proposal to keep Northern Ireland in the EU customs union – and not on Mrs May’s document.

“There will be a deal if there is an agreement on the backstop,” said Mr Barnier.

“It’s not necessarily our backstop. We can work on this, amend it, improve our backstop – the one that the Commission proposed on behalf of the Union.

“Technically we feel that it’s workable, we can improve it further, we can work on it. We are doing that work.

“But we need an operational backstop now, in the Withdrawal Agreement, and not later.”

In her first major Brexit speech since the wave of ministerial resignations which followed her Chequers deal, the Prime Minister described the white paper proposals as “a significant development of our position … a coherent package”.

And she said: “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.”

Speaking in Belfast, Mrs May also took aim at critics from the hard Brexit wing of the Conservative Party, accusing them of being ready to “betray” the people of Northern Ireland and the Republic.

She took on the argument of prominent Eurosceptics including Jacob Rees-Mogg, who say the UK should simply declare it will impose no checks on its side of the Irish border and leave it to Brussels to decide whether to require the Republic to erect barriers on the other.

“The protection of the peace process and upholding our binding commitments in the Belfast Agreement are grave responsibilities,” she said.

“Not to seek a solution would be to resume our career as an independent sovereign trading nation by betraying commitments to a part of our nation and to our nearest neighbour.”

And she 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.

Mrs May restated her implacable opposition to the EU backstop, which she said would involve the creation of a customs border within the UK, which 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, represented a “credible third option” that would “honour the Belfast Agreement, deliver on the referendum result and be good for our economy”.

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(PA Graphics)

Mr Barnier said that the Withdrawal Agreement could not be concluded without a legally binding backstop setting out the fallback arrangements if a wider solution for the Irish border could not be found.

This would be based on the Commission’s proposal but “not necessarily” stick precisely to the outline released in March, he said.