Yes. That's why I brought up my third question. Is it only an altitude within CAS we can go? The CTA part 4 (the bit we went into), is 3000-105. So my question was, is he only clearing us within CAS upto 6000' (the TA) or was he using "altitude" incorrectly as a generic term, instead of level?
EDIT in response to the above edit:
Well, really saying "no altitude XXXX" OCAS, I would consider incorrect. It's implying the controller can imply an altitude restriction, which he can't. But you still have to remain OCAS. They normally say just that "Remain clear of CAS". But as I said, they didn't today. My FI said that it was perfectly fine to go into the CTA because of that. And as I said - we were never told we busted it. Also, another club aircraft was given the same thing, and they climb above us! So if it's incorrect - NATS seriously need to issue a written notice to local based pilots and let them know - and tell their ATCOs at FF to stop using non-standard RTF (again, if it is incorrect) because it's caused some confusion - atleast on my part. :P