Donald Trump has hit back at the UK’s ambassador to Washington after leaked emails revealed he called the US president “inept” and “insecure”.
The US president said Sir Kim Darroch had "not served the UK well" and his administration was "not big fans" of the envoy.
A formal investigation will be carried out to determine how the emails from Sir Kim to the British government were leaked.
Prime minister Theresa May has “full faith” in the UK ambassador but did not agree with all of his assessment of the Trump administration, Downing Street said.
International trade secretary Liam Fox has said the leak was "unprofessional, unethical and unpatriotic", according to the BBC.
Foreign secretary Jeremy Hunt attempted to limit the damage by stressing the comments were Sir Kim's "personal opinions" and not the views of the British government.
Mr Trump - who was described as "radiating insecurity" in Sir Kim's assessment, said: "The ambassador has not served the UK well, I can tell you that.
"We are not big fans of that man and he has not served the UK well. So I can understand it, and I can say things about him but I won't bother."
Mr Hunt said Sir Kim's job was to give "frank reports" but the UK's view was that Mr Trump's administration was "highly effective".
The foreign secretary said: "It's really important to say that the ambassador was doing his job as an ambassador which is to give frank reports and personal opinions about what's happening in the country where he works, and that's his job to send back those reports but they are personal opinions, not the opinions of the British government, not my opinion.
"And we continue to think that under President Trump the United States administration is both highly effective and the best possible friend of Britain on the international stage."
The documents obtained by the Mail on Sunday detail Sir Kim's assessments of the Trump administration from 2017 to the present.
Cabinet minister David Gauke condemned the "disgraceful" leak, which will now be the subject of a Civil Service inquiry, and said ambassadors should feel able to "tell the truth as they see it".
A Foreign Office spokesman said: "A formal leak investigation has now been initiated."
Officials insisted the relationship with the White House could withstand the "mischievous behaviour" of the leak.
The diplomatic memos suggest that in order to communicate with the president "you need to make your points simple, even blunt".
In the cache of documents, Sir Kim gives a scathing assessment of the White House: "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."
He questioned whether the White House "will ever look competent".
Following Mr Trump's state visit to the UK in June, Sir Kim warned that although the president had been "dazzled" by the pomp and ceremony of the trip, his administration would remain self-interested and "this is still the land of America First".
In one of the most recent documents, Sir Kim refers to "incoherent, chaotic" US policy on Iran and questions Mr Trump's publicly stated reason for calling off a retaliatory air strike against Tehran following the downing of an American drone.
The US and Iran have been at the brink of armed conflict over tensions in the Gulf, and Mr Trump stated that he called off a planned air strike with minutes to spare because of the potentially high number of casualties.
But Sir Kim said that the explanation "doesn't stand up", and suggested it may have been motivated by Mr Trump's focus on the 2020 re-election campaign and his previous promises not to involve the US in foreign conflicts.
"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," Sir Kim said.
He said it was "unlikely that US policy on Iran is going to become more coherent any time soon" as "this is a divided administration".
In a particularly sensitive leak, a 2017 letter to the National Security Adviser Sir Mark Sedwill - sent 150 days into the Trump administration - laid bare the trouble in the White House.
Media reports of "vicious infighting and chaos" were "mostly true" despite the president's attempts to brush them off, emails said.
Referring to the early allegations of collusion between the Trump campaign and Russia, the memo said "the worst cannot be ruled out".
A lengthy investigation by Robert Mueller published earlier this year cleared the Trump team of the collusion allegations.
Justice Secretary Mr Gauke told the BBC: "I think it's very important that ambassadors give honest, unvarnished advice to their country.
"And it is disgraceful that it's been leaked."
But Brexit Party leader Nigel Farage - who the US president once suggested would make a great ambassador - said Sir Kim was "totally unsuitable for the job and the sooner he is gone the better".