“The civilised world can deal with Trump no longer. He is a gangster pirate,” he said.

The comment comes as the US president has alarmed NATO partners, saying that countries opposing an American takeover of the Danish territory could face sweeping trade penalties within weeks. Mr Trump warned that tariffs would be imposed from February 1, starting at 10% and potentially climbing to 25% by June if resistance continues.

On social media, Trump explicitly named the UK alongside France, Germany and Denmark as potential targets. The move has sent shockwaves through Europe, with economists warning that the UK could be pushed back onto “recession watch” should the measures be enacted.

Senior figures in Brussels have also reacted, with leading MEPs warning that retaliation could include freezing the EU-US trade deal. Such a move would raise the risk of another global trade war, just as fragile economies are struggling to regain stability.

Despite months of careful diplomacy aimed at keeping relations with Washington on an even keel, the Prime Minister delivered some of his most robust criticism of Mr Trump to date on Thursday night.

Sir Keir said: “Our position on Greenland is very clear – it is part of the Kingdom of Denmark and its future is a matter for the Greenlanders and the Danes.

“We have also made clear that Arctic security matters for the whole of NATO, and allies should all do more together to address the threat from Russia across different parts of the Arctic.

“Applying tariffs on allies for pursuing the collective security of NATO allies is completely wrong. We will, of course, be pursuing this directly with the US administration.”