ASA upholds complaints over misleading Linjer lab-grown diamond ads

The Advertising Standards Authority (ASA) has upheld complaints against jewellery retailer Linjer for misleading advertisements that failed to identify diamonds as laboratory-grown. 

The ruling followed challenges from the Natural Diamond Council and the London Diamond Bourse regarding two paid-for Google ads seen on 14 January 2026.

The advertisements used the terms “brilliant diamonds”, “sustainable jewellery”, and “ethically sourced gemstones”. 

However, the ASA determined that consumers would understand the word “diamond” in isolation to refer to a naturally occurring mineral. 

The regulator noted that while synthetic diamonds share chemical properties with mined stones, differences in future value make their origin material information for consumers.

Linjer stated that it did not realise the advertisements breached the CAP Code. The retailer has committed to working with its advertising agency to include specific language identifying stones as laboratory-grown and has implemented internal checks to ensure consistent terminology in the future.

The ASA assessment highlighted that the term “brilliant” describes a specific diamond cut, but the average consumer was likely to interpret the phrase “brilliant diamonds” as a general reference to natural stones. 

The regulator found that claims regarding sustainability and ethical sourcing did not sufficiently clarify that the products were synthetic.

National Association of Jewellers guidelines suggest that synthetic diamonds should be accompanied by qualifiers such as “laboratory-grown” or “laboratory-created”. 

While these guidelines are not binding, the ASA concluded that the omission of such qualifiers was misleading.

The regulator ruled that the ads breached rules on misleading advertising and qualification. 

Linjer has been instructed not to use the term “diamond” to describe synthetic products in isolation without a clear and prominent qualifier.