The US president’s latest reaction comes after the British diplomat’s unflattering assessment of White House as “inept”.

US President Donald Trump on Monday launched a broadside against UK Prime Minister Theresa May and said the United States would “no longer deal” with the British ambassador to Washington after the diplomat’s unflattering assessment of the Trump administration as “inept” were leaked to the Daily Mail newspaper.

Britain has launched an inquiry into the leak of confidential memos from the diplomat Kim Darroch that annoyed the US president and embarrassed London.

“Contact has been made with the Trump administration, setting out our view that we believe the leak is unacceptable,” May’s spokesman told reporters.

Trump responded on Twitter by criticising May’s handling of Brexit and saying she disregarded his advice.

“What a mess she and her representatives have created,” he wrote. “I do not know the Ambassador, but he is not liked or well thought of within the US. We will no longer deal with him.”

“The good news for the wonderful United Kingdom is that they will soon have a new Prime Minister. While I thoroughly enjoyed the magnificent State Visit last month, it was the Queen who I was most impressed with!” he wrote.

Hours after Trump’s tweet, May’s spokesman reiterated Britain’s position that the leak was unfortunate and said Darroch “continues to have the prime minister’s full support.”

In confidential memos to his government dating from 2017 to the present, Darroch said reports of in-fighting in the White House were “mostly true” and last month described confusion within the administration over Trump’s decision to call off a military attack on Iran.

“We don’t really believe this Administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept,” Darroch wrote in one memo.

Ministers said the government did not agree with Darroch.

Foreign Minister Jeremy Hunt, one of two men who might replace May by the end of the month, said: “I have made it clear that I don’t share the ambassador’s assessment of either the US administration or relations with the US administration, but I do defend his right to make that frank assessment.”

He promised “serious consequences” for whoever had leaked the memos.

An inquiry was under way to determine who was behind the second serious disclosure of confidential material this year. May’s spokesman said police would be involved if there was evidence of criminality.

Two months ago, May fired Defence Minister Gavin Williamson after secret discussions in the National Security Council about Chinese telecoms firm Huawei were leaked to the media, and an inquiry concluded that he was responsible.