A campaign adviser to US President-elect Donald Trump has called the incoming UK ambassador to the US, Lord Peter Mandelson, “an absolute moron”.

In a post on social media, Chris LaCivita said Lord Mandelson “should stay home”.

Mr LaCivita, who was a co-campaign manager for Trump’s presidential election bid, criticised the British government’s decision saying it was replacing a “professional universally respected ambo [ambassador] with an absolute moron”.

Lord Mandelson is one of the best-known figures in British politics, having served in multiple ministerial roles under Tony Blair and Gordon Brown before taking up a life peerage in the Lords.

He called his appointment as the UK’s next ambassador to the US as “a great honour”.