Special Armed Services (Army) Special Boat Squad (Navy). Not sure about the Airforce, don't know if they have an elite force. I'm sure if you ask the RAF they'll say that they are all elite!
The SAS is not part of the Army Air Corps. The fact that they both have the word 'Air' in their name's does not mean they are directly associated. They are two different regiments. The RAF has no 'elite' regiment.
The RAF may not have the hyped up reputation of the SAS or SBS, but the RAF regiment is one of the best equipped and most professional of all of the British regiments. Before any of you go passing judgement a battallion of the 'rock apes' could whip and of the light infantry at they're own job.