US import costs of steel and aluminium, used in everything from baseball bats to cars and aircraft parts, are expected to rise by more than $100bn after Donald Trump raised tariffs on the metals to 50 per cent this week.

The order raises import taxes for US-based firms buying from other countries from today - but the levy remains at 25% for the UK.

Unifor, Canada's private sector union, and the Aluminium Association of Canada have expressed serious concerns over the immediate impact of the tariffs.