Sir Kim Darroch has resigned as UK ambassador to the US, amid a row over leaked emails critical of President Trump’s administration.
The ambassador was branded “a very stupid guy” by the US president, after emails emerged calling his administration “clumsy and inept”.
The Foreign Office praised Sir Kim’s “professionalism and class”.
The ambassador said he wanted to put an end to speculation, adding the leak had made it “impossible” to do his job.
In a letter to the Foreign Office, Sir Kim said: “Since the leak of official documents from this Embassy there has been a great deal of speculation surrounding my position and the duration of my remaining term as ambassador.”
“I want to put an end to that speculation.”
In response to the letter Sir Simon McDonald, permanent under secretary and head of the diplomatic service, said Sir Kim had served a “long and distinguished career, with dignity, professionalism and class”.
Describing the leak as “malicious” Sir Simon added: “You are the best of us.”
Theresa May said it was a “matter of great regret” that Sir Kim felt the need to resign, saying officials needed to be able to give “full and frank advice”.
“Sir Kim has given a lifetime of service to the United Kingdom and we owe him an enormous debt of gratitude,” she added.
The prime minister said he had had the full support of the Cabinet during the row.
In a debate for the Tory leadership contest on ITV on Tuesday, frontrunner Boris Johnson repeatedly refused to say whether he would keep Sir Kim in post if he became prime minister.
But Mr Johnson said he regretted news of Sir Kim’s resignation because “he is a superb diplomat and I worked with him for many years”.
He said whoever was responsible for the leak “has done a grave disservice to our civil servants”.
Fellow candidate and Foreign Secretary Jeremy Hunt said he “profoundly” regretted the “outrageous” leak that led to Sir Kim’s departure. “It should never have come to this”, he added.
Europe Minister Sir Alan Duncan has accused Mr Johnson of throwing Sir Kim “under a bus”.
“I think for someone who wants to lead let alone unite this country, that was contemptible negligence on his part and he’s basically thrown this fantastic diplomat under a bus to serve his own personal interests,” he told the BBC.
“I’m upset and angry,” Sir Alan added.
BBC political editor Laura Kuenssberg said Mr Johnson’s lack of support for Sir Kim was “the first major act” of Mr Johnson’s hypothetical leadership.
Labour leader Jeremy Corbyn told the Commons: “The comments made about him are beyond unfair and wrong. I think he has given honourable and good service and he should be thanked for it.”
Sir Kim had been due to step down at the end of the year.
He thanked those who had offered their support, both in the UK and the US during a “difficult few days”, adding that it had “brought home to me the depth of friendship and close ties between our two countries”.
In the emails leaked to the Mail on Sunday, Sir Kim said: “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.”
The emails, dating from 2017, said rumours of “infighting and chaos” in the White House were mostly true.
Who is Sir Kim Darroch?
Born in South Stanley, County Durham, in 1954, Sir Kim attended Durham University where he read zoology.
During a 42-year diplomatic career, he has specialised in national security issues and European Union policy.
In 2007, Sir Kim served in Brussels as the UK permanent representative to the EU.
He was the prime minister’s national security adviser between 2012 and 2015, dealing with issues such as the rise of the Islamic State group in Iraq and Syria, Russian annexation of Crimea, the nuclear threat from Iran and the collapse of government authority in Libya.
He became ambassador to the US in January 2016, a year before Donald Trump’s presidential inauguration.