Chilli,
Au contraire, I said "and is provided in controlled airspace only." which I thought was quite unambiguous
I'm not sure about the RCS => "do what you're told", as according to the second point from CAP 493 an SVFR / VFR flight can choose not to comply with an RCS instruction and as for RAS must advise the controller.
Other than the meteorological conditions and controlled a/s requirements for RCS there doesn't seem to be much practical difference from RAS.
Reading between the lines I think that an RCS instruction that is not compiled with by an SVFR/VFR flight means the controller must plan otherwise; for an RAS it is the pilot who becomes responsible for separation if not complying with an instruction.
Yack!