It's all here
Denti, he is talking GA types, not a mult crew EFIS/FMS jet like yours or mine.
The guidance material from the CAA is here for ga
http://www.caa.co.uk/docs/33/CAP773.pdf
Also interesting reading
http://www.terps.com/ifrr/jan97.pdf
RAIM is for the approach phase, terminal and en route. Doesn't your ops manual containing the PRNAV approval say anything about RAiM for PRNAV arrivals etc? Our FMS's are using DME/DME, DME/VOR and so on as well as GPS and or inertial. Hence, for RNAV arrivals and departures not required, but PRNAV I believe it is. It's possible your ops people do a ground based RAIM prediction for you. If GPS equipped, I believe it's criteria to alert crew if RAIM is lost, you're boxes may be more intelligent than mine and do it for you?
One airport example is EKCH 10_2 F
Willing to learn!
All the best mate.