It seems that the 1 for every 50 seats (not pax) as described by BEagle is the norm. However wide bodied aircraft (like the Voyager) require I CC for every door exit (rather than window o/wing exits) or 1 for every 50 seats, whichever is the greater. Hence the 8 required for Voyager.
There are some aircraft that require more than these minimum numbers, each type having the certificated requirement stated. The 737 mentioned earlier has a minimum of 3 or 4 depending on seat numbers (B737-400/3, B737-800/4). These numbers can vary with the country of registration.
LJ, of course QR's don't list Cabin Crew Flying Badges, because the RAF doesn't award them yet. Hence this lengthy thread! We still have the anomaly whereby the military regulator (the MAA) describes Cabin Crew as aircrew, to which Flying Badges are normally awarded, but the RAF doesn't recognise them as aircrew, preferring to characterise them as a Ground Trade and to which it is presently recruiting :-
https://www.raf.mod.uk/recruitment/r...ground-steward