These tariff threats have cast doubt on King Charles's anticipated state visit to the US in April, which aims to revitalise trade relations.
Liberal Democrats leader Ed Davey urged the Prime Minister to tell Trump that the King's visit should be cancelled if the tariffs proceed.
Sir Keir Starmer criticised Trump's use of tariffs against allies as “completely wrong” and not the way to resolve differences.
Starmer avoided advising the King directly on the visit, stressing the importance of a strong US relationship for security, while acknowledging differences of opinion.