Britain's ambassador to Washington resigned on Wednesday after Donald Trump labelled him "stupid" and "wacky" following the release of confidential memos from the envoy in which he branded the us president's administration inept.
"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", he wrote.
"I think it's very important we should have a close partnership, a close friendship with the United States", said Johnson, whom Trump has praised in the past.
Diplomatic sources said Sir Kim Darroch used a phone call with the Tory leadership favourite to tell him that his refusal to support him in his row with Donald Trump was "a factor" in his shock decision to quit.
"Kim Darroch did an outstanding job as Ambassador and sorry to see he has resigned his post".
"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", Kim Darroch said in his resignation letter.
Diplomatic memos he had written were released earlier this week questioning whether the White House "will ever look competent" under Mr Trump and referring to its "incoherent, chaotic" foreign policies.
In one of the cables published in Britain last weekend, the 65-year-old Darroch said, "We don't really believe this administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction driven; less diplomatically clumsy and inept".
She said that Boris Johnson's failure in the debate to stand up for Sir Kim "spoke volumes". "Like I've said, sometimes a great story is just that; not some kind of global conspiracy".
"I want all our public servants to have the confidence to be able to do that and I hope the House will reflect on the importance of defending our values and principles, particularly when they are under pressure".
Trump had no immediate comment on Darroch's departure.
He said he regretted how an "outrageous leak caused this".
Darroch has received support from across the British political spectrum. The respected diplomat's move has caused Britain's relations with the United States presidency to sink to its lowest levels in decades.
It underscored that the close relationship between the two countries has become increasingly lopsided - a severe problem as the United Kingdom prepares to set a new path with its departure from the European Union. The fracas not only highlighted Trump's now well-established hypersensitivity to any kind of criticism - even in what is widely seen in the diplomatic community as boilerplate reports that ambassadors send home - but also underscored Trump's public intervention in British politics and the British right-wing Brexiteers embrace of Trump.
"It is shameful that Kim Darroch has effectively been forced out for doing the job that diplomats are appointed to do", Scottish First Minister Nicola Sturgeon tweeted.