President Donald Trump tore into Britain's US envoy Tuesday, calling Ambassador Kim Darroch "a very stupid guy" after his secret diplomatic cables critical of the president and his administration were leaked to the press.
Prime Minister Theresa May said on Wednesday that 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". Darroch's forthright views - meant for consumption behind closed doors - have caused embarrassment between two countries who often celebrate having a "special relationship".
Trump responded by insulting May and calling Darroch "wacky".
Trump's devastating tweets sent a clear message to London that Darroch, a career diplomat who was on Monday branded an anti-Trump globalist by his foes back home, is no longer welcome in the White House.
"I do not know the Ambassador, but he is not liked or well thought of within the U.S. we will no longer deal with him".
Darroch has served as Britain's envoy to Washington since 2016, and the cables cover a period from 2017 to recent weeks.
The Intercept's Robert Mackey wrote Tuesday that "the president's angry denunciation of the previously obscure diplomat. was so predictable, it looked to some observers like the intended outcome of a plot, hatched in London, to depose the ambassador in Washington by leaking his confidential briefing notes".
Sir Kim Darroch has come under fire after some of his communications with London were leaked, detailing his concern over the state of Trump's administration.
But the tweets by Trump, which followed a similar social media barrage on Monday, ratcheted up pressure on Britain's government.
It comes less than 24 hours after Mr Trump tweeted that he was "very critical" of Theresa May over the "mess she and her representatives have created" regarding Brexit.
However, he was never particularly in favour with Trump himself, who publicly suggested that the then Ukip leader, Nigel Farage, should be May's choice - forcing her spokesman to clarify that: "There is no vacancy".
His opponent in the race for the prime ministership, current foreign minister Jeremy Hunt, meanwhile, called on Trump to "respect" the United Kingdom, insisting Darroch would stay in his post if he was to succeed May.
He said it was unprecedented for a head of state, friendly or hostile, to refuse to work with British ambassadors, and the last time there had been a problem with an envoy to the United States was in 1856.
That broadside against Britain and its leader, long a staunch USA ally, drew a sharp rebuke Tuesday from British Foreign Secretary Jeremy Hunt, who said Trump's comments were "disrespectful and wrong".
Former foreign minister Johnson, a hardliner on Brexit, is the favorite to replace May in the leadership contest against Hunt.
With an Andy Warhol screenprint of the Queen behind him, Darroch would make toasts at such events with plenty of quips.
"I think it's very important we should have a close partnership, a close friendship with the United States", he said.
But there was anger among many British politicians that Darroch had been forced out, said junior foreign minister Alan Duncan, who blamed Johnson.
"You can't change an ambassador at the demand of a host country", Hague told the BBC.