Prime Minister Theresa May said she regretted that Britain's ambassador to the United States had felt the need to resign, adding that officials needed to be able to give "full and frank advice". "The whole cabinet rightly gave its full support to Sir Kim on Tuesday".
The timing of the discord comes as Britain is hoping to strike a major trade deal with its closest ally after it leaves the European Union, an exit scheduled for October 31.
Britain is hoping to strike a major post-Brexit trade deal with Washington as one of the upsides of leaving the bloc.
The resignation has infuriated London's diplomatic and political class. It called the leak "mischievous behavior" and said the public has expected diplomats to provide honest assessments of the politics in the countries where they're posted.
Johnson expressed his regret at Sir Kim's departure, describing him as a "superb diplomat" who he had worked with for many years.
Pointing out that "loyalty is a two-way street", Sir John said: "I do not think that is good for the morale of the civil service and I do not think anybody who does that will endear themselves in obtaining the loyalty of the civil service in future".
"It is shameful that Kim Darroch has effectively been forced out for doing the job that diplomats are appointed to do", Scotland's First Minister Nicola Sturgeon tweeted. "He deserves to look back upon his career as a servant of Britain with the greatest satisfaction and pride".
The envoy said that, although his posting being due to end later this year, he believed it would be better to leave early.
"I know of none", Sir Simon replied.
"Somebody has, for whatever malicious reasons, sought to either damage the UK-US relationship or indeed Sir Kim personally. I don't think that's the right thing to do. but let's face it, our relationship with the USA is of fantastic importance". "This is a disgraceful example of what "taking back control" truly looks like: pandering to bigoted foreign leaders and letting them dictate the fate of United Kingdom ambassadors", David Lammy, a lawmaker from the opposition Labour party, wrote on Twitter.
Sir Alan, another Hunt supporter, said Mr Johnson was an "utter wimp when the crunch comes when he should be making a stand". Any other White House would have overlooked the ambassador's undiplomatic language rather than damage relations with a close US ally.
"For someone who wants to lead, let alone unite, the country, that was contemptible negligence on his part", he told the BBC. The head of Britain's diplomatic service, Simon McDonald, said it was the worst breach of trust he had seen in his career.
The mood inside the British Residence is one of incredible sadness. "What they are in detail I can't tell you this afternoon", he said. "This is the last thing you want in the relationship between two very close allies".