US President Donald Trump says he "will no longer deal" with the British ambassador to the United States, after a news report that the UK diplomat had described Mr Trump's administration as dysfunctional, clumsy and inept.
"I do not know the Ambassador, but he is not liked or well thought of within the U.S. We will no longer deal with him," Mr Trump said in a Twitter post that also criticised outgoing Prime Minister Theresa May.
Memos from Kim Darroch, ambassador to Washington, were divulged to a British newspaper.
In the confidential memos to his government dating from 2017 to the present, Mr 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 strike 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," Mr Darroch wrote in one memo.
Mr Trump had dismissed the ambassador on Sunday as not having "served the UK well."
Britain's government has told Washington that leaks of the memos were a matter of regret, May's spokesman said on Monday.
"Contact has been made with the Trump administration, setting out our view that we believe the leak is unacceptable," Prime Minister Theresa May's spokesman told reporters. "It is, of course, a matter of regret that this has happened."
Trade minister Liam Fox, who is visiting Washington, told BBC radio he would apologise to Mr Trump's daughter Ivanka, whom he is due to meet.
"I will be apologising for the fact that either our civil service or elements of our political class have not lived up to the expectations that either we have or the United States has about their behaviour, which in this particular case has lapsed in a most extraordinary and unacceptable way," he said.
"Malicious leaks of this nature ... can actually lead to a damage to that relationship, which can therefore affect our wider security interest."
The revelations come at a time when Britain is hoping to strike a major trade deal with its closest ally after it leaves the European Union, an exit currently scheduled for 31 October.
Ministers said the government did not agree with Mr Darroch, although Mrs May's spokesman said she had full faith in him.
Foreign minister Jeremy Hunt, one of two men who might replace Mrs 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 who had leaked the memos, telling reporters: "What we will not allow to happen is any interruption in the superb relationship that we have the United States, which is our closest ally around the world."
Nigel Farage, leader of the Brexit Party and long a thorn in the side of British governments, said figures such as Mr Darroch would be "not be around" if ex-foreign minister Boris Johnson, the other candidate seeking to replace Mrs May, was chosen by Conservative Party members.
Despite being close to Mr Trump, Mr Farage ruled himself out of becoming Britain's next ambassador in Washington.
"I don't think I'm the right man for that job," he told BBC radio.
An inquiry is now being held to determine who was behind the disclosure. May's spokesman said if there was evidence of criminality, then the police would be involved.
Mr Trump also criticised Mrs May.
"What a mess she and her representatives have created. I told her how it should be done, but she decided to go another way," he said. "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.