Although still not an officially accepted as a main "AT" activity it can be added to AT packages if authorised in writing by the CO, and he also authorises the person taking the activity as "competent".
I suspect that his has just recently changed, maybe due to the amount of pretty serious accidents.
The place to get clarification is your Bde G3 Adv Tng bloke, failing that a call to LAIT or TAIT will advise.
Once again the Army caught short, The RAF had identified this "Hole" in the JS scheme and have there own providers.
The Army failed to recognise Mountain Biking, and then when it did acknowledge the activity by providing bikes for AYTs and CTTs it allowed groups to be supervised by holders of MLT + First Aid cert.
The SMBLA/British Cycling is the recognised NGB that the RAF are using to provide.