Donald Trump has said the UK will “probably not” get a trade deal with the US, if the prime minister’s Brexit plan goes ahead.
He told The Sun the PM’s plan would “probably kill the deal” as it would mean the US “would be dealing with the European Union” instead of with the UK.
Theresa May has been making the case for a US free trade deal with Mr Trump, on his first UK visit as president.
She said Brexit was an “opportunity” to create growth in the UK and US.
Mr Trump also said he hoped the former foreign secretary Boris Johnson would rejoin the government, saying he was a “great representative for the UK”.
He and his wife were given a red carpet reception at Blenheim Palace, Oxfordshire on Thursday evening.
They were at a black-tie dinner with Mrs May as news broke of his interview with the newspaper.
The president told The Sun newspaper that the UK’s blueprint for its post-Brexit relations with the EU was “a much different deal than the people voted on”.
On the subject of a future trade deal, he said the Chequers deal would mean it would be “most likely … we would be dealing with the European Union instead of dealing with the UK, so it will probably kill the deal”.
He said he had told Mrs May how to do a Brexit deal, but: “She didn’t agree, she didn’t listen to me.”
“I told her how to do it. That will be up to her to say. But I told her how to do it. She wanted to go a different route,” he said.
The US president also said he was “cracking down” on the EU because “they have not treated the United States fairly on trading”.
On Thursday, the UK government published its proposal for its long-term relationship with the EU.
The long-awaited plan is aimed at ensuring trade co-operation, with no hard border for Northern Ireland, and global trade deals for the UK.
But leading Brexiteers, Boris Johnson and David Davis, resigned from the cabinet days after ministers reached agreement on the plan at Chequers a week ago.
Mr Johnson launched a scathing attack on the PM’s strategy, saying the “dream is dying, suffocated by needless self doubt”.
Responding to an earlier suggestion by President Trump that the British people were not getting the Brexit they voted for, Mrs May said: “We have come to an agreement on the proposal we are putting to the European Union which absolutely delivers on the Brexit we voted for.”
Analysis, by BBC political editor Laura Kuenssberg
From the moment of his election, Donald Trump was an awkward friend for Theresa May.
He runs towards a fight. She does everything in public to avoid one.
Well, just before they were due to appear alongside each other on UK soil he publicly, and at length, gave a “both barrels” verdict on her most important policy.
At Thursday’s dinner, Mrs May said that more than one million Americans work for UK-owned firms, telling Mr Trump: “As we prepare to leave the European Union, we have an unprecedented opportunity to do more.
“It’s an opportunity to reach a free trade agreement that creates jobs and growth here in the UK and right across the United States.”
As Mr Trump arrived in the UK, protesters gathered outside the US ambassador’s residence in in Regent’s Park, London, and an estimated 1,000 of them demonstrated near the palace, the birthplace of wartime Prime Minister Winston Churchill.
John Rees of the Stop the War group addressed protesters, saying of Trump: “He’s a wrecking ball for race relations, he’s a wrecking ball for prosperity, he’s a wrecking ball for women’s rights, he’s a wrecking ball for any peace and justice in this world and we have to stop him.”
On Friday, Mrs May and Mr Trump will go to watch a joint counter-terrorism exercise by British and US special forces at a military base.
The pair will then travel to Chequers – the PM’s country residence in Buckinghamshire – for talks with the foreign secretary.
Extra security is in place to police the protests. More are planned for the second day of Mr Trump’s visit.
The president and first lady will travel to Windsor on Friday afternoon to meet the Queen, before flying to Scotland to spend the weekend at Mr Trump’s Turnberry golf resort. This part of the visit is being considered private.