David Lammy backed Lord Mandelson after speculation Donald Trump could block his appointment as US ambassador.

The Foreign Secretary insisted the Labour grandee is the “right man for this moment” as Mr Trump returns to the White House.

He said: “Peter Mandelson is a man of considerable expertise. He’s the right man for this moment to be our ambassador.

“He’s been a business secretary, a Northern Ireland secretary, of course he’s worked in the European Commission, and he brings all of that to bear, working as our ambassador in the United States.

“And of course he’s looking forward to presenting his credentials to Donald Trump.”

There were reports that the Trump administration could be considering not granting approval to Lord Mandelson as the UK’s ambassador to the US.

Mr Lammy also praised the US president-elect despite previously being one of his fiercest critics and once branding him a “racist and KKK/neo-Nazi sympathiser”.

Asked if he had changed his mind, he told BBC Radio 4’s Today programme: “In this role, I’ve said that the approach has got to be progressive realism, and that is that you meet the world as it is, not as you would wish it to be.

He added: “The Donald Trump I met … had incredible grace, generosity, very keen to be a good host, very funny, very, very, very friendly, very warm, I have to say, about the UK, our royal family, Scotland.”

The Foreign Secretary said Mr Trump believed in the US being “strong and powerful” but he was “not a man who, in any sense, is a warmonger”.

He said he sees Mr Trump as a “revisionist actor” who “wants to change the rules of the game” and seems very focused on the possibility of normalising Saudi relations with Israel, which he said can only come if there is a path to a two-state solution in the Middle East.

It comes as the US president-elect will be sworn in to his second term in the White House today.