In the UK, any person that deals in precious metals must display on their premises, in a conspicuous position, a Hallmarking Act 1973 notice as approved by the British Hallmarking Council.
The most current Hallmarking Dealer’s Notice is below. Currently, all Silver items over the weight of 7.78g, and any gold items over the weight of 1g must be hallmarked by law.
London Hallmark dealer notice