There are two separate problems that both get called “fake hallmarks,” and they are not the same problem. One is a genuine mark being misread — 18KGP actually means 18 carat gold plating, and nobody is lying by stamping it. That is covered in the hallmark reference and the is it real gold guide. This one is about the other problem: a mark that is not genuine at all, applied to make a piece look like something it is not. In the UK, that is a specific criminal offence, defined precisely enough that it is worth knowing the actual definitions rather than a vague sense of “fake.”
The three things the law actually calls hallmark fraud
The UK’s Hallmarking Act 1973 governs this, at section 6. It does not describe one offence called forgery — it lists several distinct acts, because a hallmark can be faked in more than one way and the law wanted each one covered.
- Striking a counterfeit die or mark — making a punch, or a stamp, that copies a genuine assay office or sponsor’s mark, with intent to defraud or deceive. This is the most literal reading of “fake hallmark”: a mark that was never struck by a real assay office at all.
- Removing a mark to transpose it — cutting a genuinely hallmarked section out of one piece and moving it onto another, or fixing a mark that has already been removed from something else onto a new item. The trade sometimes calls this sweating. The mark itself is completely real; it has simply been relocated onto metal the assay office never tested.
- Uttering or possessing a counterfeit — supplying, offering, or simply having a counterfeit die or a marked article in your custody, without lawful excuse, while knowing or believing it to be counterfeit.
On indictment, the maximum penalty is imprisonment for up to ten years — the same order of seriousness the law attaches to counterfeiting currency, not a labelling technicality. As originally passed in 1973, summary conviction carried a fine capped at £400; the indictable route is the one that reflects how seriously this is actually treated today.
Why this is specifically a UK-shaped problem
A hallmark can only be counterfeited where there is a real one to copy. UK, Irish and most European systems have an assay office physically test the metal and strike its own mark alongside the maker’s — an independent, legally backed record of what the metal is. In the US and most of the rest of the world, the maker stamps the purity themselves and nobody checks it. Overstating purity there is fraud too, but it is not hallmark fraud in this specific legal sense, because there was no independent mark to forge in the first place — only a maker’s own claim, which is a different thing to fake.
What each kind of fraud actually looks like on a piece
A cast copy, mark and all
The simplest version: someone takes a mould from a genuinely hallmarked piece and casts a copy in base metal or lower-purity alloy. The hallmark comes along for the ride as part of the casting, because it was in the mould. The giveaway is texture rather than reading the numbers — a struck hallmark is crisp, with sharp edges cut into the metal; a cast copy of one is softer, slightly rounded, and often a fraction smaller than the genuine article it was copied from, because metal shrinks slightly as it cools.
A transposed panel
Sweating leaves a physical seam, because two pieces of metal have been joined that were not originally one piece. Under magnification, look for a border around the hallmarked area — a colour change, a grain line, or a join that catches the light differently to the surrounding metal. On flatware this sometimes shows as a hallmark panel that sits slightly proud of the surface around it, because it was let into a piece it does not quite match.
Marks that do not agree with each other
A genuine British hallmark is a set — sponsor’s mark, fineness mark, assay office town mark, and usually a date letter — all struck at the same time, in the same style, to the same depth. The hallmark reference shows what each town mark and standard mark actually looks like. If one element in the set looks noticeably fresher, more worn, or struck at a different depth than the others, or if the date letter’s typeface and shield shape do not match what that assay office used in the year it claims, the set has likely been assembled rather than struck together.
What actually settles it
None of the checks above is a verdict — they are reasons to look closer, in the same way the home checks in the is it real gold guide can only rule things out. The authority that can actually confirm or deny a UK hallmark is the assay office that struck it, and any of the UK’s assay offices can examine a suspect piece. That is a different service to a jeweller’s quick weight-and-magnet check, and it is the one that carries legal weight if a piece turns out to be exactly what this guide describes.