At this stage i don't know who'll be enforcing this and who won't, but if it's anything like the Brake lever then it's possible all TDOs will end up enforcing it.From 1 March 2022 back protectors will become essential for those wishing to ride on track, in the same way that front brake lever guards are required for your pride and joy, we believe you should ride with the best available equipment to reduce the risks of serious injury if an accident were to occur.
Please also note that in an update to circuit and insurance regulations, from the same date, a motorcycle licence will now be required at all circuits; however at Anglesey, Croft, Lydden and Mallory Park we will accept restricted/A1 licences as well as any valid ACU discipline licence as proof of competency. At MSV circuits, as has been the case for a number of years, they will continue to require either a full DVLA motorcycle licence or a valid ACU Road Race licence.
It doesn't however specify who's checking it and to what level they do or don't need to pass to be accepted.