You should have a look around an OACC one day Notso .. might be educational.
No where near 50 airlines in the PRM scheme, nearer a dozen who account for about 80% of the traffic. Majority rules in the OCA !!
PS Ask BA Ops how it is done, sure they'll be pleased to let you know the real story and also maybe give you an insight in to PRMs
Failing that, you could read the NAT MNPSA Ops Manual
NAT MNPSA Manual
Pages 18 and 31 are the relevant ones.