Yup, me too on the AJS 37A-T, always a good weekend. doesn't help with identifying your frame though, that swing arm design is interesting, and the method of chain adjustment/clamping the spindle. Definitely not Cheetah, had one until recently, (it'll be at Priddy), Greevesrob suggested Kyffin Sapphire, I've never seen one in the flesh, only a picture from a sales brochure (on the Otter website I think?) but could be. Elstar built a few trials frame too I believe, again check out the Otter BSA website, lots of good info on there.
Jeff