Boris Johnson will fly to the continent tomorrow and is set on a collision course with EU leaders after they rejected his demand to scrap the Irish backstop.

Brussels issued a damning dismissal of Mr Johnson’s call to scrap the policy, while Angela Merkel said a “practical solution” would have to be found without reopening the withdrawal agreement negotiated by Theresa May.

Mr Johnson had sent a letter to EU officials calling for the Irish border backstop to be removed from the Brexit withdrawal agreement but presented no alternative to the policy.

Donald Tusk, the president of the European Council, effectively accused the prime minister of wanting to wind the clock back on the Northern Ireland peace process, as well as deception.

“The backstop is an insurance to avoid a hard border on the island of Ireland unless and until an alternative is found,” Mr Tusk said on Tuesday. “Those against the backstop and not proposing realistic alternatives in fact support reestablishing a border. Even if they do not admit it.”

A spokesperson for the European Commission told reporters in Brussels that the executive body was in full agreement with Mr Tusk’s comments.

“You will also have seen that President Tusk has just tweeted his initial reaction to this letter, a reaction that we share,” the spokesperson said.

“From the commission side we welcome the UK government’s engagement and a continued commitment to an orderly withdrawal. We firmly believe that this is in the best interests of the EU and the UK.

“However, we also note that the letter does not provide a legal operational solution to prevent the return of a hard border on the island of Ireland, it does not set out what any alternative arrangements could be, and in fact it recognises that there is no guarantee that such arrangements will be in place by the end of the transitional period.”

Guy Verhofstadt, the European parliament’s chief Brexit representative, also joined in the coordinated response from EU institutions, warning: “I don’t see any majority in the European parliament to remove the backstop from the withdrawal agreement. It is a vital insurance policy, negotiated in good faith and supported by the people of the island of Ireland. The time for bluster and political blame games is fast running out.”

“It is a question of the declaration on future ties,” German chancellor Ms Merkel said during a visit to Iceland ahead of her meeting with Mr Johnson in Berlin. “And I think we will act in a very unified way.”

Donald Tusk, the European Council president (AFP/Getty) (AFP/Getty Images)

Mr Johnson will make his debut on the world stage as prime minister this week. He is heading to Berlin on Wednesday and Paris on Thursday to meet with Ms Merkel and French president Emmanuel Macron separately. The prime minister is expected to try to make the case for dropping the backstop, which is hated by Tory MPs and the Northern Irish unionists who prop up his minority government.

The prime minister has said he is “confident” that the EU will change its stance on the backstop. The EU has repeatedly said that the withdrawal agreement cannot be reopened.

Responding to Mr Tusk’s comments, a Downing Street spokesperson said: “We are deeply invested in the peace, prosperity and security of Northern Ireland and always will be and we have been clear that we will never place infrastructure, checks, or controls at the border.

“But it is clear that unless the withdrawal agreement is reopened and the backstop abolished there is no prospect of a deal. It has already been rejected three times by MPs and is simply unviable as a solution, as the PM’s letter makes clear.

“We are ready to negotiate, in good faith, an alternative to the backstop, with provisions to ensure that the Irish border issues are dealt with where they should always have been: in the negotiations on the future agreement between the UK and the EU.”

Steve Barclay, the Brexit secretary, spoke with Michel Barnier and senior Irish politicians on Tuesday.

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“I reconfirmed we’re unequivocally committed to the Belfast (Good Friday) Agreement and that we want a deal, but parliament has been clear it won’t accept the backstop,” he said following the discussion.

“As the PM Boris Johnson explained to the European Council president Donald Tusk in this letter, that means the backstop must go. There’s a strong shared desire for a deal in London, Belfast, and Dublin.”

The minister added that he wanted to work “constructively on alternative arrangements” for the Northern Irish border but restated the prime minister’s pledge that “we’re leaving the EU on 31 October come what may”.

Michelle O’Neill, Sinn Fein’s leader in the Northern Irish assembly, who also spoke to Mr Barclay said: “I told him they are playing fast and loose with our livelihoods.