Britain's ambassador to the US predicted Sir Keir Starmer could be ousted if the local elections are a bloodbath for Labour. Sir Christian Turner, who replaced Lord Mandelson in the top Washington job, admitted the Prime Minister was "pretty clearly on the ropes" and his future looked "quite touch and go" at one point in February.

In leaked remarks to British students visiting the US that month, he highlighted that Labour's rules to remove a sitting PM require 80 MPs to "sign a letter in public, which is like signing a death warrant". Sir Christian noted that Sir Keir was "a stubborn guy" and unlikely to quit.

But in the comments reported by the Financial Times, he added: "The moment I would look to is the May elections. If Labour does very badly ... I suspect the party will be able to go over that threshold and remove him – seems to me to be the conventional thinking."

The highly embarrassing remarks for the Prime Minister have emerged as the King is making a state visit to the US.

Sir Christian also played down the special relationship between the UK and the US.

He said it was “quite nostalgic, it’s quite backwards-looking, and it has a lot of baggage about it".

He added: “I think there is probably one country that has a special relationship with the United States – and that is probably Israel.”

A Foreign Office spokesman said: "These were private, informal comments made to a group of UK sixth-form students visiting the US in early February.

"They are certainly not any reflection of the UK Government's position."