French President Emmanuel Macron has fired a warning shot at Boris Johnson ahead of their meeting in Paris.

He has insisted the Prime Minister’s demands to reopen the Brexit deal are “not an option” and suggested that the UK risks heading towards a future of being a vassal state to Donald Trump’s USA if it chooses to prioritise ties with Washington over a close relationship with the European Union.

Mr Johnson will meet Mr Macron on Thursday for talks which are likely to be less encouraging than his meeting with Angela Merkel.

The UK Government was buoyed on Wednesday after comments by the German Chancellor which seemed to indicate that European leaders could be willing to consider alternatives to the Irish backstop in a bid to avoid a no-deal Brexit.

Hosting the Prime Minister at the Chancellery in Berlin, Mrs Merkel set Britain a 30-day deadline for coming up with an alternative solution to replace the Irish backstop – a bid to avoid a hard border in Northern Ireland after the UK’s exit from the European Union by keeping Britain aligned with certain regulations set by Brussels.

But Mr Macron told reporters on Wednesday night that the demands to renegotiate the Brexit deal are “not an option”.

He said: “We have to help the British deal with this internal democratic crisis but we mustn’t be hostage to it nor export it.”

Mr Johnson is expected to meet US President Mr Trump at the G7 summit in Biarritz which starts on Saturday, but Mr Macron warned that the UK would be a “junior partner” in its relationship with Washington after a hard Brexit.

France now views a no-deal Brexit as the most likely outcome, according to diplomatic sources in Paris.

“Can the cost for Britain of a hard Brexit – because Britain will be the main victim – be offset by the United States of America? No,” Mr Macron said.

“And even if it were a strategic choice, it would be at the cost of a historic vassalisation of Britain.

“I don’t think this is what Boris Johnson wants. I don’t think it is what the British people want.”

The frank comments could make the Prime Minister’s trip to the Elysee Palace a dicey affair, with the Conservative Party leader set to meet his French counterpart for lunch at his official residence to discuss changing the terms of Britain’s exit.

Mr Johnson flew to Paris after a three-course dinner with Mrs Merkel, an evening that a Downing Street spokesman called “constructive”.

Number 10 was pleased with the tone of the German Chancellor’s comments and sees her 30-day deadline as an attempt to get the ball rolling on addressing fears of Britain leaving without a deal.

Speaking at the press conference on Wednesday, Mrs Merkel said: “If one is able to solve this conundrum, if one finds this solution, we said we would probably find it in the next two years to come but we can also maybe find it in the next 30 days to come.

“Then we are one step further in the right direction and we have to obviously put our all into this.”

Mr Johnson said he was “more than happy” with the timetable proposed by his German counterpart.

Boris Johnson and Angela Merkel
The two leaders held a joint press conference (Stefan Rousseau/PA)

“I must say I am very glad listening to you tonight, Angela, to hear that at least the conversations that matter can now properly begin,” he replied.

“You have set a very blistering timetable of 30 days – if I understood you correctly, I am more than happy with that.”

The PM told Mrs Merkel that the backstop would have to go as part of further discussions – or else Britain is prepared to leave without a deal.

He said the “whole and entire” backstop would need to be removed before a deal could be reached.

But Mr Johnson, on his first trip to Germany as PM, said he was optimistic an agreement could be struck.

“What, in my experience, happens is that people find a way through and I think that, if we approach this with sufficient patience and optimism, as I say, we can get this done and it is in the final furlong generally when the horses change places and the winning deal appears,” he told the press.

The visits to Berlin and Paris will not be the only international trips that Mr Johnson will make this week.

He will be back in France at the weekend to take part in the G7 summit which is being held in Biarritz on the country’s south-western coast.