Britain expressed its regret to Washington on Monday for the leak of confidential memos in which its ambassador described US President Donald Trump's administration as "dysfunctional" and "inept".
The memos from Sir Kim Darroch, UK ambassador to Washington, were published by the Mail on Sunday, annoying Trump and embarrassing London.
"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 told BBC radio. He said he would apologise to Trump's daughter Ivanka, whom he is due to meet as he visits Washington.
"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."
Bad timing for London
The revelations come at a time when Britain is hoping to strike a major trade deal with its closest ally after it leaves the EU.
Trump told reporters, of Darroch: "We are not big fans of that man and he has not served the UK well, so I can understand and I can say things about him but I won't bother."
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 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."
What was in the leaked memos?
Ambassador Kim Darroch reportedly said Trump's presidency could "crash and burn" and "end in disgrace", in the cache of secret cables and briefing notes sent back to Britain seen by the Mail on Sunday
"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 allegedly wrote in one dispatch.
The paper said the most damning comments by Darroch described Trump, who was received by Queen Elizabeth II during a state visit to Britain just last month, as "insecure" and "incompetent".
A memo sent following the controversial visit said the president and his team had been "dazzled" by the visit but warned Britain might not remain "flavour of the month" because "this is still the land of America First".
'Vicious infighting and chaos'
He reportedly wrote that the "vicious infighting and chaos" inside the White House -- widely reported in the US but dismissed by Trump as "fake news" -- was "mostly true".
Darroch is one of Britain's most experienced diplomats whose posting in Washington D.C. began in January, 2016, prior to Trump winning the presidency.
The Mail on Sunday said the memos, likely leaked by someone within Britain's sprawling civil service, cover a period beginning in 2017.
In one of the most recent reported dispatches filed on June 22 Darroch criticised Trump's fraught foreign policy on Iran, which has prompted fears in global capitals of a military conflict, as "incoherent" and "chaotic".
He allegedly said the president's assertion, that he called off retaliatory missile strikes against the Iranian regime after a US drone was shot down because it risked killing 150 Iranians, "doesn't stand up".
"It's more likely that he was never fully on board and that he was worried about how this apparent reversal of his 2016 campaign promises would look come 2020," Darroch reportedly stated, referring to the next presidential election.
Foreign office does not dispute veracity of memos
Britain's Foreign Office did not dispute the veracity of the memos.
"The British public would expect our ambassadors to provide ministers with an honest, unvarnished assessment of the politics in their country," a spokeswoman said.
"Their views are not necessarily the views of ministers or indeed the government," she added, noting "we pay them to be candid".
"Our team in Washington have strong relations with the White House and no doubt that these will withstand such mischievous behaviour," the spokeswoman said of the potential fallout from the leak.