Animal rights group PETA could take the Ministry of Defence (MoD) to court in a row over the fur used for the King's Guards' bearskin caps.
PETA developed a faux fur version of the black bearskin famously worn by guards outside Buckingham Palace and claims the MoD failed to properly consider the alternative.
The group has filed for judicial review, claiming MoD failed to adhere to its own procedures, behaved unfairly, breached procedural expectation, and exhibited flawed decision-making, amounting to unlawful conduct.
PETA claims the MoD's refusal to trial the faux fur or evaluate the findings of laboratory testing is in breach of a promise it made to replace the bearskin once a suitable alternative is found.
PETA and the MoD are at odds over whether the faux fur, developed with the textile manufacturer ECOPEL, meets MoD's requirements.
The MoD previously claimed the faux fur failed to meet four of the five requirements it set for artificial fur, relating to water absorption, penetration, appearance, drying rate and compression.
But PETA argues tests by a fabric technologist show its product meets and, in some cases, exceeds these requirements, and claims the MoD has refused to evaluate the results.
Lorna Hackett, PETA's legal representative from Hackett & Dabbs LLP, said: "We are seeking the court's intervention so that the MoD fully evaluates the report and reaches a fresh decision by fair process, with a view to considering the faux fur fabric's adoption as a replacement for real fur if it is found to be suitable, as the MoD has long committed to doing."
An MoD spokesperson said: "We have been served with a legal claim in respect of this matter and cannot provide specific comment on ongoing legal proceedings."
PETA has lobbied for the caps' fur to be replaced with a synthetic substitute since 2002, accusing the MoD of "support for the slaughter of Canadian black bears".
The MoD claims the furs are not "hunted for order", come from legal, licenced hunts and has said that cutting its orders would not reduce the numbers being hunted.
The caps are worn by foot soldiers in the Grenadier Guards, the Coldstream Guards, the Scots Guards, the Irish Guards and the Welsh Guards.