Police have held “initial discussions” over an investigation into the leak of diplomatic memos from Sir Kim Darroch, the UK’s ambassador to the US, who has now resigned.
The deepening diplomatic rift between the UK and US President Donald Trump saw Sir Kim quit his post in Washington earlier.
He said the furore over the leaked messages, in which he called Mr Trump “inept”, was making it “impossible” for him to carry out his duties.
The US president had responded to the revelation of Sir Kim’s memos by branding the diplomat “wacky” and “a very stupid guy”, as well as vowing to “no longer deal with him”.
Sir Kim’s resignation came just before Theresa May took Prime Minister’s Questions in the House of Commons.
She revealed to MPs her “great regret” at Sir Kim’s resignation, adding: “Good government depends on public servants being able to give full and frank advice, and I want all our public servants to have the confidence to be able to do that.
“I hope that the House will reflect on the importance of defending our values and principles, particularly when they are under pressure.”
Downing Street later revealed the government has held “initial discussions” with the police over a Whitehall investigation into the leak.
“If there was concern about criminal activity the police would become involved more formally at that point,” a Number 10 spokeswoman said.
Metropolitan Police Commissioner Cressida Dick confirmed her force had been “alerted” to the inquiry, but added the government had yet to refer the matter to Scotland Yard.
Offering her personal viewpoint, Ms Dick expressed her “regret” at the leak, adding: “I obviously think it’s very sad to somebody like Sir Kim resigning in this manner.
“I also think that as a citizen… it is a deeply worrying situation where communications like this can end up in the public domain.”
The most senior civil servant at the Foreign Office, Sir Simon McDonald, admitted he was “bracing” himself for more leaks of diplomatic messages.
“I fear there may be more,” Sir Simon said, as he told the Commons’ foreign affairs committee that “nothing like this has ever happened before, there must be consequences”.
The top official added the last time Britain had “difficulty” with the US over its ambassador was in 1856, when its diplomat was accused of recruiting Americans to fight on the British side in the Crimean War.
Anger at Westminster over the growing row centered on Boris Johnson’s refusal to commit to keeping Sir Kim in post during a televised Conservative leadership debate on Tuesday night.
Whitehall sources told Sky News that Sir Kim “decided the game was up” following the lack of support from Mr Johnson, who is expected to succeed Mrs May as prime minister later this month.
Foreign Office minister Sir Alan Duncan, who is supporting Foreign Secretary Jeremy Hunt over Mr Johnson in the Conservative leadership race, told Sky News that Mr Johnson had “basically thrown [Sir Kim] under the bus”.
“I think that the conduct of Boris Johnson has discredited him enormously in the eyes of many people in this country,” Sir Alan said.
Mr Hunt himself said it was “absolutely essential” for the UK to defend its diplomats when they “do their job”.
“In this situation we had a fine diplomat who was just doing what he should have been doing, giving a frank assessment, a personal assessment of the political situation in the country that he was posted,” he said.
“That’s why I defended him and I think we all should.”
Labour leader Jeremy Corbyn chose not to ask a single question about the diplomatic row during PMQs.
But shadow foreign secretary Emily Thornberry later issued a statement to claim Sir Kim had been “bullied out of his job because of Donald Trump’s tantrums and Boris Johnson’s pathetic lick-spittle response”.
Following Sir Kim’s resignation, Mr Johnson claimed whoever was responsible for leaking the diplomatic memos had “done a grave disservice to our civil servants”.
“I hope that whoever it is, is run down, caught and eviscerated, quite frankly, because it is not right that advice to ministers that civil servants must be able to make in a spirit of freedom should be leaked,” he said.
“It is not right that civil servants’ careers and prospects should be dragged into the political agenda.”
Defence minister Tobias Ellwood claimed the “diplomatic discord” between the UK and US was “unprecedented in modern times”.
He posted on Twitter: “The rapid & very public escalation, culminating in the resignation of a respected senior diplomat, raises serious questions- not least about the quality of critical back channels with our most trusted & valued ally.”
On the other side of the Atlantic, Sir Kim found support from US senators, with Republican Linsey Graham countering the views of his president by tweeting: “Kim Darroch did an outstanding job as Ambassador and sorry to see he has resigned his post.
“He got a raw deal from press.”
Mark Warner, the Democrat vice chairman of the Senate intelligence committee, posted: “@KimDarroch was an outstanding Ambassador who served his country with honesty and integrity.
“He was a true friend to the United States, and it’s a shame to see him go.”