The resignation of Kim Darroch came a day after Trump lashed out at him on Twitter describing him as "wacky" and a "pompous fool" after leaked documents revealed the envoy's dim view of Trump's administration.
"If that's the case I think it's clear that Boris Johnson is effectively behaving as Donald Trump's patsy and he's doing that clearly because he is banking on a sweetheart trade deal and is putting himself in hock to the USA president", the spokesman told reporters.
Mr. Johnson has a close relationship with Mr. Trump and the U.S. President has spoken highly of him. Trump had tweeted soon after he was elected in 2016, and that sentiment seemed to be part of the set-up that sent Darroch packing.
Sir Nigel Sheinwald, a former ambassador to the U.S., said he believed Mr Johnson's comments may have played a part in Sir Kim's decision to go.
"I wouldn't use the language President Trump used, and I wouldn't agree with it", he said.
On Sunday, the Daily Mail published a series of leaked memos written by Darroch that characterized the president as "inept" and "clumsy" and warned that Trump's "career could end in disgrace".More news: Springbok World Cup victor James Small dies aged 50
On Tuesday, Hunt condemned Trump's outbursts as "disrespectful and wrong".
Sir Kim also thanked those in the United Kingdom and U.S. who had offered him support since the leak and that he was "deeply touched".
"I don't think he got the support he needed from across our political class".
Darroch said his position had become untenable. "The person responsible is the person who leaked this", said Michael Fallon, a Tory MP who backs Mr. Johnson.
Like his predecessors, Darroch was a prominent figure in Washington, meeting frequently with high-level United States officials and hosting parties at the stately British Embassy.
"I think it's very important we should have a close partnership, a close friendship with the United States", Johnson said.More news: Tucker Carlson Calls 'Annoying' Ilhan Omar Proof Immigration Is 'Dangerous' To US
It's unclear whether May will have time to name a replacement before she leaves office later this month. Darroch often addressed the attendees at such gatherings, making sure to single out high-level administration officials.
Sir Kim resigned this afternoon saying his position had been made "impossible" after Donald Trump said the USA would not deal with the ambassador who described his administration as "inept".
Appointing ambassadors usually involves a formal civil service process with advertisements, applications and interviews, though Simon McDonald, head of Britain's diplomatic service, said the post of ambassador to the US wasn't always chosen that way.
"He has basically thrown this fantastic diplomat under the bus to serve his own personal interests".
And while Boris Johnson's hesitation in backing him was a factor in Darroch's resignation, it was not the main reason.
Trump himself had previously suggested that Nigel Farage, now leader of the Brexit Party, would be a good choice as ambassador, irritating British officials.More news: Borderlands 3 Has an Apex Legends-Style Ping System
"The right decision, time (to) put in a non-Remainer who wants a trade deal with America", Farrage tweeted. "History shows that there are often bespoke procedures for filling the embassy in Washington, DC", he said.