Sir Keir Starmer appointed Lord Mandelson because he wanted an “unconventional ambassador” for the Trump administration, a Cabinet minister has said.

The Scottish Secretary Douglas Alexander said No 10 “knew this was an unconventional presidential administration” when it chose to make Lord Mandelson the British ambassador to the US.

The Scottish Secretary told Sky News: “There was a political judgment made by the Prime Minister that Peter Mandelson, given his unique experience in trade, was well qualified to support and advance the UK interests in what we judge was going to be an absolutely central aspect of the relationship between the Trump administration and the British Government.”

Sir Keir is now facing a Labour revolt after emails emerged showing Lord Mandelson had urged Jeffrey Epstein to fight for early release from jail.

His dismissal on Thursday came after The Telegraph revealed Lord Mandelson worked with Epstein on a £1bn business deal after his conviction.