They do seem beloved of the "press ups" on spinning bikes and other niff naff stuff not particularly related to biking in any spinning class I've been in which is why I've never continued with it. I know its not much help to you but in the Preston area there is (or was) a series of spinning classes run from a cyclists perspective (i.e they were chuffing hard) by a competitive cyclist unfortunately I couldn't make it. They were advertised in the local serious roadie shop. It may be worth contacting some "serious" bike shops or local competitive cycling clubs/tri clubs as they may know something. There must be something in London.