The only alternative to a “hard Brexit” is no Brexit, European Council president Donald Tusk has warned Theresa May.
In a strongly-worded intervention, Mr Tusk insisted that the UK would not be able to retain the benefits of EU membership after Brexit and the only alternative is the UK remaining within the EU.
Speaking in Brussels, Mr Tusk said the proposals for leaving the European Union outlined in the referendum campaign meant radically loosening ties with the rest of the bloc - a “de facto hard Brexit”.
He warned that the process would be “painful” and predicted both the UK and EU would lose out as a result of Brexit.
But he insisted there could be “no compromises” over single-market access, stressing that freedom of movement would remain a condition - despite claims from Foreign Secretary Boris Johnson that he expected European leaders to back down.
Mr Tusk told the European Policy Centre that the Brexit campaign's demand to “take back control” - with the UK outside EU jurisdiction, no freedom of movement and no contributions to Brussels' budget - had “definitive consequences” for the Government and the negotiation process.
“This means a de facto will to radically loosen relations with the EU, something that goes by the name of hard Brexit.
“This scenario will, in the first instance, be painful for Britons.”
He dismissed Mr Johnson's “cake philosophy” - being “pro-having it and pro-eating it” - as “pure illusion”.
“The brutal truth is that Brexit will be a loss for all of us,” Mr Tusk said. “There will be no cakes on the table for anyone. There will be only salt and vinegar.”
Mr Tusk said it was “useless to speculate about soft Brexit”, where the UK would retain the closest possible ties to the bloc after leaving.
“In my opinion the only real alternative to a hard Brexit is no Brexit, even if today hardly anyone believes in such a possibility,” he told the European Policy Centre.
He said he would defend the interests of the 27 remaining members of the EU but “I am afraid that no such outcome exists that will benefit either side”.
Mr Tusk held open the possibility of the UK going back on the referendum result, saying it would be for the UK to assess the outcome of the negotiations and “determine if Brexit is really in their interest”.
The council president added that other EU leaders would be sympathetic if the UK Government reversed the Brexit decision.
“If we have a chance to reverse this negative process, we will find allies,” he said.
Mr Tusk said the Article 50 process could be halted by Ms May's Government even once it had been triggered.
His comments came as Mr Johnson came under fire after suggesting that Britain can get a Brexit trade deal that is “of greater value” to the UK economy than access to the EU single market.
The Foreign Secretary told MPs that the concept of the single market was “increasingly useless”, as the UK sought to extend its trade links around the world.
But critics of “hard Brexit” warned that loss of access would harm British businesses by denying them a marketplace of 500 million consumers free of tariffs and regulatory obstacles to trade.
Giving evidence to the House of Commons Foreign Affairs Committee, Mr Johnson conceded that negotiating a new relationship might take longer than the two years envisaged under Article 50 of the EU treaties. But he insisted he was “absolutely confident” that a good deal would be reached.
Mr Tusk also suggested the timetable was “optimistic”, adding “I think the process will be much longer than two years.”
Responding to Mr Johnson's comments, Conservative former minister Anna Soubry, of the Open Britain campaign, said: “If there's a deal of 'greater value' out there than single market membership, then businesses and economists have not come across it. The Government needs to provide concrete evidence before it pulls us out of our home market of 500 million customers.”
Mr Johnson said he thought Britain had done “the right thing” in voting to leave the EU on June 23, and told the committee: “I think those who prophesied doom before the referendum have been proved wrong and I think they will continue to be proved wrong.
“Obviously it will take time before the full benefits of Brexit appear.”
He insisted that Britain can remain a “lodestar and magnet” for talented migrants from around the globe even after it introduces tougher immigration rules following Brexit.
And he suggested he expects European leaders to back down on their insistence that access to the single market is dependent on allowing free movement of people.
“The idea that the Brownian movement of individuals, of citizens across the surface of Europe, is somehow there on tablets of stone in Brussels is a complete nonsense,” said Mr Johnson. “It's a fiction.
“We are taking back control of our borders as we said we would, and that's what we will do.
“It doesn't mean that we are going to be hostile to people of talent who want to live and work here. I think it is extremely important that we continue to send out a signal of openness and welcome to the many brilliant people who help to drive the London economy and the UK economy.”
Press Association