Britain's ambassador to Washington Kim Darroch announced on Wednesday his resignation after drawing U.S. President Donald Trump's ire for criticizing his administration in leaked confidential cables to London.

"The current situation is making it impossible for me to carry out my role as I would like," Darroch wrote in his resignation letter. "I believe in the current circumstances the responsible course is to allow the appointment of a new ambassador." 

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Memos from Kim Darroch were leaked to a British Sunday newspaper, infuriating Trump who launched a stinging Twitter attack on both the envoy and British Prime Minister Theresa May who had given him her full support. 

Below are extracts from Darroch's resignation letter: 

"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. The current situation is making it impossible for me to carry out my role as I would like.

"Although my posting is not due to end until the end of this year, I believe in the current circumstances the responsible course is to allow the appointment of a new ambassador. 

"I am grateful to all those in the UK and the U.S. who have offered their support during these difficult few days. This has brought home to me the depth of friendship and close ties between our two countries. I have been deeply touched."

"I am also grateful to all those with whom I have worked over the last four decades, particularly my team here in the U.S. The professionalism and integrity of the British civil service is the envy of the world. I will leave it full of confidence that its values remain in safe hands."

"Sir Kim (Darroch) will step down once a new appointment has been made (...) The new appointment will be made in due course," May's spokesman told reporters.

May regrets Darroch's resignation 

May told parliament after the resignation was announced that she had spoken to Darroch, who was due to leave his post anyway at the end of the year. 

"I have told him it is a matter of great regret that he has felt it necessary to leave his position as ambassador to Washington," she said. "The whole cabinet rightly gave its full support to Sir Kim on Tuesday."

Simon Mcdonald, the head civil servant at Britain's Foreign Office, said he accepted Darroch's resignation with deep personal regret. 

"Over the last few difficult days you have behaved as you have always behaved over a long and distinguished career, with dignity, professionalism and class. 

"The Prime Minister, Foreign Secretary and whole of the public service have stood with you: you were the target of a malicious leak; you were simply doing your job. 

"I understand your wish to relieve the pressure on your family and your colleagues at the Embassy; I admire the fact that you think more of others than yourself. You demonstrate the essence of the values of British public service." 

Johnson calls Darroch a superb diplomat 

Darroch is a superb diplomat and public servants should not be dragged into the political agenda, Boris Johnson, the frontrunner to become prime minister, said on Wednesday. 

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Johnson, a former foreign secretary, repeatedly failed to back Darroch during a televised debate late on Tuesday. 

But during a campaign visit on Wednesday, Johnson said of him: "he is a superb diplomat," adding that whoever leaked the documents "really has done a grave disservice to our civil servants, to people who give impartial advice to ministers." 

"It is not right that civil servants' careers and prospects should be dragged into the political agenda," Johnson said. 

Hunt 'outraged' by leak which led to envoy quitting 

Britain's foreign secretary Jeremy Hunt said on Wednesday he was outraged that confidential memos by the country's ambassador to the United States were leaked, leading to envoy Kim Darroch's resignation from his post. 

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"Whenever I visited Washington as foreign secretary, I was struck by Sir Kim's professionalism and intellect," Hunt – who is a contender to be Britain's next prime minister – said in a statement. "I am outraged that a selection of his reports should have been leaked." 

What happened?

The Mail on Sunday's publication of Darroch's cables set off a political firestorm in London and saw Trump launch two successive days of Twitter attacks against the envoy and May.  

One of the cables called the Trump administration "uniquely disfunctional" and another characterised the U.S. leader as "inept" and "insecure."  

Trump tweeted Monday that Darroch "is not liked or well thought of within the U.S. We will no longer deal with him." He also welcomed the "good news" that Prime Minister Theresa May was stepping down in two weeks.  

The U.S. leader followed that up on Tuesday by calling "wacky Ambassador" Darroch "a very stupid guy." The scandal saw Darroch taken off the guest list of a dinner attended by Trump on Monday.  

He also missed visiting UK Trade Minister Liam Fox's talks in Washington on Tuesday with the president's adviser and daughter Ivanka Trump. 

(With input from Reuters and AFP)