Look for the Hallmark, It's Your Guarantee.

A hallmark is a set of marks applied to precious metals (gold, silver, platinum or palladium) which identifies the type of precious metal the item is made from as well as the seller/maker of the item (person/company), the date the marks were applied and by which Assay Office. In the UK, it is a legal requirement for any items (over a certain weight) being sold as being made of precious metals, to be sent to one of four Assay Offices for testing/hallmarking. For Ditsy Pincers jewellery, the hallmark is applied by the The Goldsmiths’ Company Assay Office, London.

Please see below from the British Hallmarking Council for more information: