In my experience it's very common not to be positively told 'radar control service' on entering CAS. Brize, for example, usually just say 'entering controlled airspace' plus a reminder of the clearance conditions (e.g. 'maintain VMC, not above 1200ft Brize QNH 1012'). In fact, I think I've only ever been told 'radar control service' explicitly by Lyneham when entering the CTA.
It's good to have that confirmed, though, Chilli. I told my passenger on Friday that we were under RCS (he's a NPPL pilot and was rather enjoying the experience of IFR which was new to him!) so I'm glad I was right...
Tim