Theresa May appeared to back down on Thursday in her fight to choose Britain's next ambassador to the US after her foreign minister hinted that an early appointment was unlikely.

Although a Downing Street spokesman would only confirm that Sir Kim Darroch’s replacement would be announced “in due course”, Sir Alan Duncan admitted: “We do really want to make sure we get the very best person and I think it'd be a pity if in the interests of alacrity we chose a number two rather than a number one.”

It came after Sir Alan, minister of state for Europe and the Americas, had accused Tory leadership favourite Boris Johnson of throwing the veteran diplomat “under a bus” by failing to back him during a TV debate with rival Jeremy Hunt on Tuesday night.

Sir Kim announced on Wednesday he was standing down from his posting in Washington, saying his position had become "impossible" following a barrage of abuse from President Trump following the revelation he had sent diplomatic cables describing the Commander-in-chief as "inept".