LONDON — President Trump on Thursday intervened directly in Britain’s fraught debate over withdrawal from the European Union, saying that Prime Minister Theresa May’s plans to keep close economic ties with the bloc could “kill” a possible trade deal with the United States.
In an interview with The Sun, Mr. Trump also said that Mrs. May had ignored his advice on negotiations over Britain’s departure, known as Brexit.
“I would have done it much differently,” Mr. Trump was quoted as saying. “I actually told Theresa May how to do it, but she didn’t listen to me.” Instead she went “the opposite way,” and the results have been “very unfortunate,” he said.
Mr. Trump also said that Boris Johnson, a Brexit hard-liner who resigned from Mrs. May’s government this week, would make “a great prime minister.”
Mrs. May has been making the case for a free trade deal with the United States and argued that Brexit was an “opportunity” to deepen trans-Atlantic ties and spur economic growth both in Britain and in the United States. British officials hoped that Mr. Trump’s visit would help that process.
Instead the comments are likely to stoke acute tension within Mrs. May’s Conservative Party, following the publication on Thursday of the government’s plan for exiting the bloc, which would keep Britain tied to European Union rules on goods and agricultural products.
Even before it was released as a white paper on Thursday, that proposal had prompted the resignation of three government ministers, including Mr. Johnson, the foreign secretary who had argued for a cleaner break with the European Union.
Before arriving in Britain, Mr. Trump had described Mr. Johnson as a friend and said he might be in contact with him during the presidential visit to Britain, which began on Thursday and is scheduled to end on Sunday.
Mrs. May’s new plan is designed to minimize the economic impact of Brexit which could be severe because the European Union is Britain’s biggest trading partner. But Mr. Trump appeared to side with pro-Brexit critics who argue that, by keeping many of the European Union’s economic rules, it would inevitably reduce the scope for a separate trade deal with the United States.
“If they do that, then their trade deal with the U.S., will probably not be made ” Mr. Trump said, according to the paper.
The comments are acutely sensitive because supporters of Brexit argue that one of the key advantages of quitting the European Union would be that it would leave Britain free to strike trade deals around the world.
When he resigned on Monday Mr. Johnson made a fierce attack on Mrs. May’s strategy for Brexit saying the “dream is dying, suffocated by needless self doubt”.