Donald Trump said Ambassador Kim Darroch had "not served the UK well"

US President Donald Trump hit back on Sunday and the UK launched an inquiry after leaked memos revealed Britain's ambassador in the US had described the president and his White House as "inept" and "uniquely dysfunctional".

Trump said Ambassador Kim Darroch had "not served the UK well" and that he and his administration were "not big fans" of the envoy.

Darroch had said Trump's presidency could "crash and burn" and "end in disgrace", according to a cache of secret cables and briefing notes sent back to Britain seen by the Mail on Sunday newspaper.

"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".

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".

Asked about the leak, Trump told reporters in the US: "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."

The UK foreign ministry said it would carry out a formal investigation into the leak.

Jeremy Hunt, the foreign minister, distanced himself from Darroch's remarks, saying: "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."

From 2017 to now

Darroch is one of Britain's most experienced diplomats whose posting in Washington 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.

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.