Hallmarking.
The laws apply to EVERYTHING sold in the UK, that is made of gold, platinum, silver and sterling silver, regardless of where it may have been manufactured and whether it does, or does not contain stones or gems. The only exemptions, (covered by the above exemption laws stated above), are items that fall beneath the specific weight thresholds. The thresholds are 1 gram for gold, 7.78 grams for silver and 0.5 grams for platinum.
If you sell an item of gold that weighs more than 1 gram, or an item of sterling silver that weighs more than 7.78 grams, or an item of platinum that weighs more than 0.5 grams, the piece by law MUST be hallmarked.
A hallmark is NOT 925 ! Please refer to https://www.gov.uk/government/publications/hallmarking-guidance-notes/hallmarking-is-the-law-guidance-summary that explains in detail, what a hallmark is and just how many components form a hallmark. 925 stamped on a piece of sterling silver, is NOT a hallmark.
Any piece I design which is falls into the hallmarking category will of been sent to London Assay office and carry a full hallmark.