Boris Johnson is set for showdown Brexit talks in Paris - hours after French President Emmanuel Macron ruled out making concessions.
The UK Government was buoyed on Wednesday after comments by German Chancellor Angela Merkel which seemed to indicate that European leaders could be willing to renegotiate the Withdrawal Agreement in a bid to avoid a no-deal Brexit.
Hosting Prime Minister Mr Johnson at the Chancellery in Berlin, Ms 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 that the demands to renegotiate the Brexit deal were "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 Macron added: “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.
"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 Mr Johnson'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 his three-course dinner with Mrs Merkel, an evening that a Downing Street spokesman called "constructive".
Downing Street was pleased with the tone of the German Chancellor's comments and see 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, Ms 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.
"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."
Mr Johnson told Ms Merkel that the backstop would have to go as part of further discussions - or else Britain was prepared to leave without a deal.
He said the backstop would need to be removed "whole and entire" 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.