Kim Darroch was sucked into a row this week after his private memos were leaked to a British newspaper, showing that he had described the Trump administration as inept.

Trump responded with a scathing Twitter attack on both the envoy and outgoing prime minister Theresa May, who had given Darroch her full support.

Johnson was criticised by lawmakers in his own party for failing to support Darroch during a televised debate this week, just hours before the envoy resigned.

A diplomatic source told Reuters that Johnson's lack of support had been one factor in his decision. However Johnson said Darroch had not watched the debate but had heard an inaccurate account of what was said.

"He said that what somebody had relayed to him had certainly been a factor in his resignation," he told BBC TV. "I think unfortunately what I said on that TV debate was misrepresented to Kim."