"Lab-grown diamond" is not a legally defined term in a single UK statute. What exists instead is a layered set of rules, and by 2026 the regulators have applied them to lab-grown diamonds often enough that the practical position is clear.

1. The CAP Code and the ASA: the word "diamond" needs a qualifier

The UK Code of Non-broadcast Advertising (the CAP Code), enforced by the Advertising Standards Authority, prohibits misleading advertising (rule 3.1), misleading omissions (3.3) and qualifications that contradict the main claim (3.9). The ASA has now applied these rules to lab-grown diamonds three times.

Skydiamond, 10 April 2024. On a complaint from the Natural Diamond Council, the ASA found that The Sky Mining Company's ads used "diamonds", "diamonds made entirely from the sky" and "Skydiamond" without an explicit qualifier such as "synthetic", "laboratory-grown" or "laboratory-created". Survey evidence cited by the ASA suggested about a quarter of UK respondents were unaware synthetic diamonds existed. The ASA also ruled that the FAQ line "Each Skydiamond is a perfectly formed real diamond" was misleading, because "real" implies geological origin 1 6.

Novita Diamonds and Linjer, 13 May 2026. Two further complaints, from the Natural Diamond Council and the London Diamond Bourse, were upheld. Novita's Meta ads promoted "ready-to-ship engagement rings" without saying the diamonds were synthetic; the ASA held that "consumers would understand the word 'diamond' in isolation to mean a naturally occurring mineral consisting of crystallised carbon" and breached rules 3.1, 3.3 and 3.9 2. Linjer's Google ads ("Discover our brilliant diamonds") were treated the same way; the ASA said the disclosure had to be in the advert itself, not only on the website it linked to 3 4.

CAP guidance, 23 October 2025. Between the two sets of rulings CAP published advice for lab-grown advertisers: qualifiers must be "clear, prominent and consistent" throughout the copy; "diamond" alone is not enough; "real diamond" should be avoided; and an environmental descriptor such as "carbon neutral diamond" does not count as disclosure because it does not say the stone was grown 5. CAP also said a consumer should not be able to go from a homepage to checkout without an explicit indication that the diamond is synthetic 5.

The ASA regulates advertising, not the sale itself, and its sanctions are reputational. But its rulings are the clearest public statement of what UK regulators think "diamond" means to an ordinary consumer.

2. Consumer law: the DMCC Act 2024 (which replaced the 2008 Regulations)

For the sale itself, the relevant law was for many years the Consumer Protection from Unfair Trading Regulations 2008. On 6 April 2025 those Regulations were repealed and replaced by Part 4 of the Digital Markets, Competition and Consumers Act 2024, which carries over the prohibitions on misleading actions and misleading omissions and gives the Competition and Markets Authority direct power to fine traders without going to court 7 8. Selling a lab-grown diamond without telling the buyer what it is would be a misleading omission of material information under that Act. Trading Standards enforce locally.

3. The NAJ Diamond Terminology Guideline: assured advice

The trade's own rulebook is the National Association of Jewellers' Diamond Terminology Guideline, drawn up in 2018 with CIBJO, the Natural Diamond Council, the Responsible Jewellery Council and others. In December 2020 Buckinghamshire and Surrey Trading Standards, the NAJ's Primary Authority partner, granted it "assured advice" status, meaning a retailer who follows it can expect Trading Standards across the UK to recognise that it is describing diamonds correctly 9. The Guideline's position is that the unqualified word "diamond" means a natural diamond; a lab-grown stone must be described with the qualifier "laboratory-grown", "laboratory-created" or "synthetic" on all point-of-sale material, invoices and labels 10.

4. The Hallmarking Act 1973: metal only

Buyers sometimes assume a UK hallmark vouches for the whole piece. It does not. The Hallmarking Act 1973 makes it an offence to describe an article as gold, silver, platinum or palladium, above small weight exemptions, unless it has been tested and marked by one of the four UK Assay Offices 11 12. The Act is silent on gemstones. Your lab-grown engagement ring in 18ct gold must be hallmarked for the gold; nothing in that mark tells you what the stone is. The Assay Offices now sell separate diamond-verification services precisely because hallmarking does not cover the stone 13.

What a UK retailer must therefore tell you

Putting the layers together, a UK retailer selling a lab-grown diamond should:

  • use "laboratory-grown", "laboratory-created" or "synthetic" (or the accepted short form "lab-grown") every time the word "diamond" appears, in adverts, on the product page, on the label and on the receipt;
  • never describe the stone as a "real", "genuine" or "natural" diamond, or as simply "a diamond";
  • not rely on an environmental or brand term to do the job of disclosure;
  • supply a grading report from an independent laboratory that itself says "laboratory-grown" (see reading a lab-grown certificate);
  • hallmark the metal.

A retailer who does all of this is meeting the law. One who does not is, at best, advertising in breach of the CAP Code and, at worst, committing a misleading omission under the DMCC Act.