Puts tongue firmly in cheek.....
Keep the RAF, but take all of their helicopter capability from them. Give the helo's to the FAA (they are the only ones who know how to operate the damn things in rough weather). Take fast jets from FAA and leave the RAF to play with them and the troop transports.
Army and RM only get scouts and Apache so they can give CAS.
So RM/Army CAS for troops and tank busting.
RAF for fast jets/bombers, troop transport and cargo.
RN for Sub hunting/SAR/Troop deployment (note to crabs, this also means pickup)
Clear borders for all services and no doubling up on roles. RAF get aircraft and training to deploy on carriers regularly (so they can do some weekend work for once) RN and Army work close together on Joint ops SUPPORTING each other.
Everyones a big happy family.
Or we go the route of the USMC. Disband the RAF and Army, kick out everyone who is not good enough to wear the Green Beret 99.9% and let Royal play with all of the toys. If Royal can manage to do so well with crap kit, just imagine what it could achieve with a good budget and nice shiny whizz bangs.