China dominates the world’s supply of such minerals and the magnets made from them that are used in cars, airplanes, robots and semiconductors.

U.S.-China trade talks this week, however, confirmed this was a miscalculation.

Under the terms of the UK-US pact, Trump agreed to cut a 27.5 per cent tariff on cars to 10 per cent for the first 100,000 vehicles shipped from the UK, in a move that was widely welcomed by auto grou...