The UK would face a better prospect of avoiding US tariffs on steel and aluminium after leaving the European Union, Donald Trump indicated last night.

Mr Trump announced a 25 per cent tariff on steel, and 10 per cent on aluminium, to begin in two weeks' time.

He exempted, at least temporarily, Mexico and Canada, and suggested the "great country" of Australia would also be spared, along with "possibly other countries as well" who were "real friends".

Mr Trump indicated those nations spending more on defence would be better positioned, and White House officials indicated "carve outs" would be decided on a "country by country" basis.

The UK is one of only half a dozen Nato countries that meets the requirement of spending two per cent of GDP on defence. The others are the US, Poland, Estonia, Greece and Romania.

British ministers are understood to have contacted their American counterparts and Whitehall sources are confident that UK firms could ultimately avoid the tariffs.

However, the announcement is expected to be the beginning of a wider trade war, with additional tariffs likely to follow.