Sir Keir Starmer has "utterly rejected" the idea that the UK must choose between the US and EU when Trump returns to the White House.
During a speech at the Lord Mayor's Banquet in London, the prime minister said the UK would "never turn away" from its relationship with the United States, whilst promising to build stronger bonds with Europe.
He used his first major foreign policy speech to say that the relationship between Britain and the US had provided the “cornerstone of our security and prosperity for over a century."
However, he also stressed the world faced "dangerous time," and that Ukraine must now be put in the "strongest possible position" before any negotiations over a peace deal with Russia takes place.
The prime minister later described Putin as an “erratic, increasingly desperate aggressor."
"Against the backdrop of these dangerous times, the idea that we must choose between our allies, that somehow we’re with either America or Europe, is plain wrong," he said.
"I reject it utterly. Attlee did not choose between allies. Churchill did not choose.
"The national interest demands that we work with both."
However, speculation remains that Donald Trump may launch a trade war against Europe and reduce support for Ukraine, which could put the UK under pressure to take sides.