Police have been urged to investigate the leak of sensitive diplomatic messages which showed the UK’s ambassador to Washington believed Donald Trump’s administration to be “inept”.

Downing Street said Theresa May has “full faith” in Sir Kim Darroch after the extraordinary breach of confidentiality triggered a political firestorm on both sides of the Atlantic.

Conservative Tom Tugendhat, chairman of the Commons Foreign Affairs Committee, told MPs he had written to the Metropolitan Police Commissioner Cressida Dick to “ask that a criminal investigation also be opened into the leak”.

And Foreign Office minister Sir Alan Duncan said police could be involved if evidence of wrongdoing over the leak is found, telling the Commons: “If evidence of criminality is found, then yes, the police could be involved.”

While showing support for the ambassador and the need for “unvarnished assessments” of foreign political situations, Number 10 distanced itself from Sir Kim’s withering assessment of the Trump White House.

The Prime Minister’s official spokesman told a Westminster briefing on Monday morning: “The PM has full faith in her ambassador to Washington.

“Our ambassadors provide honest, unvarnished assessments of politics in their country, those views are not necessarily the views of ministers or indeed of the Government.

“As the Foreign Secretary has said, this leak is not acceptable.

“We would expect such advice to be handled in the correct way and a leak inquiry has been launched.”

Sir Simon McDonald, Permanent Secretary at the Foreign and Commonwealth Office, told the Public Accounts Committee that “significant damage” had been caused by the leak.

US Presidential election
Sir Kim Darroch, the UK’s ambassador to Washington (Anthony Devlin/PA)

Asked if Mrs May agreed with the contents of Sir Kim’s leaked assessment of the Trump administration, the spokesman said: “The PM does not agree with that assessment.”

Earlier, International Trade Secretary Liam Fox called for the law to be involved in how the explosive and supposedly secret remarks from the British ambassador to the US became public.

Mr Fox expressed concern the leaks could damage the UK’s relationship with Washington after Mr Trump made clear his displeasure with Britain’s chief envoy to the US.

Mr Trump hit out at the UK’s ambassador to Washington after the leak of sensitive diplomatic messages painting an unflattering assessment of his administration.

The president said Sir Kim had “not served the UK well” and his administration were “not big fans” of the envoy.

Mr Fox, who is visiting the US, told the BBC: “This is such a damaging, potentially damaging, event that I hope the full force of our internal discipline, or even the law, will come down on whoever actually carried out this particular act.”

A formal investigation will be carried out to determine how the candid and highly embarrassing messages from Sir Kim to the UK Government were leaked.

Mr Trump, who was described as “radiating insecurity” in Sir Kim’s assessment, was clearly annoyed by the leak.

He told reporters: “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.”

Foreign Secretary Jeremy Hunt said he did not agree with all the views expressed by Sir Kim and insisted Britain has the “warmest” of relationships with the US.

Speaking at a press conference at the Foreign Office, Mr Hunt said: “It’s a personal view and there will be many people in this building who don’t agree with that view and indeed I don’t agree with some of the views that we saw in those letters.

US President Donald Trump and the Queen during the state banquet at Buckingham Palace
Donald Trump and the Queen during the state banquet at Buckingham Palace (Dominic Lipinski/PA)

“I think the US administration is highly effective and we have the warmest of relationships and a partnership based on standing up for shared values.”

The documents obtained by The Mail On Sunday detail Sir Kim’s assessments of the Trump administration from 2017 to the present.

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”.

It is the second major leak inquiry in Government this year, and comes after Gavin Williamson was sacked as defence secretary over his alleged involvement in the leak of information about Chinese tech giant Huawei.