Originally Posted by
TheFlyingDoctor
G class is group bookings (more than nine passengers, so can't quote through normal mechanisms; a tour operator might book you into this even if your own party is smaller), staff 'hotlines', and (I think) some BA Holidays fares.
G is also offered for BA domestic and short haul daytrips - they added some cheap day trip economy return fares which book in to G class a few years ago. I have had G class several times this way.