Brexit has shown that leaving the EU comes at an "exorbitant price", France's finance minister said, as he suggested some Brexit politicians were liars.
Bruno Le Maire said leaving the single market "can of course be done" but at a price which could economically "end up with a nightmare".
His comments at a conference in Paris on reforming the global trade system came as Theresa May battled to save her draft agreement for Britain's divorce from the UK.
Mr Maire said: "There are many lessons to be learned from this political situation.
"What does Brexit show? A simple thing, that leaving the European single market simply has an exorbitant economic price."
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Calling the single market a "considerable force" in global trade, he warned that Britain could face "economic disaster" if it leaves.
"It can of course be done," he added.
"Every nation is free to decide to exit the single market and the European Union but what Brexit shows is that the economic price to exit the single market is exorbitant and that there are some politicians who are liars, irresponsible who in Great Britain explained to the British people that Brexit would end with better days to come.
"The truth is that, economically, Brexit could end with a nightmare."
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Meanwhile, the Austrian Chancellor Sebastian Kurz praised the draft Brexit text ahead of a meeting with EU Council President Donald Tusk.
"It's a good deal for both sides, nobody was tricked into it, but this deal prevents a hard Brexit.
"It helps us in Europe, but it helps Britain even more. A hard Brexit would hurt Great Britain much more.
"I sincerely hope there will be some necessary support in the British parliament that would lay the foundation for an orderly withdrawal, that at the same time we can live together in an orderly way."
In the UK the draft Brexit text sparked a flurry of resignations from the government even as it was rubber-stamped by the cabinet on Wednesday evening.
Among those who quit were Dominic Raab, Mrs May's Brexit secretary and work and pensions secretary Esther McVey.
More than 20 Tory MPs publicly said they have sent a letter of no confidence to Sir Graham Brady, chairman of the influential Tory backbenchers 1922 Committee.
If he receives 48 a leadership vote would be triggered.
But the prime minister has remained defiant, saying she believes the draft deal is the "right one for our country".
She told a press conference on Thursday evening: "I believe with every fibre of my being that the course I have set out is the right one for our country and all our people.
"Leadership is about taking the right decisions, not the easy ones.
"As PM, my job is to bring back a deal that delivers on the vote of the British people, that does that by ending free movement... ensuring we are not sending vast annual sums to the EU any longer, ending the jurisdiction of the European Court of Justice, but also protects jobs and protects people's livelihoods, protects our security, protects the union of the United Kingdom.
"I believe this is a deal which does deliver that, which is in the national interest, and am I going to see this through? Yes."