Legal
Stable belts were never part of the uniform - they were an optional, buy yourself, add on and so the wearing should/could never be enforced (in the same way that the RAF cummerbund is an option to a sqn/stn/unit cummerbund or the waistcoat for Mess Kit). That, I believe, is still the case (but may have changed recently - blues not being part of day to day London rig I tend to give uniform a mild ignore
- with the introduction of the "new" (copied from the Rocks) stable belt with metal buckle).