Special Service Group ORBAT 1943 - 1945:
Special Service Group
1 Special Service Brigade (UK - Normandy - Europe)
3 Cdo
4 Cdo
6 Cdo
45 (RM) Cdo
2 Special Service Brigade (Middle East - Italy)
2 Cdo
9 Cdo
40 (RM) Cdo
43 (RM) Cdo
3 Special Service Brigade (Far East)
1 Cdo
5 Cdo
42 (RM) Cdo
44 (RM) Cdo
4 Special Service Brigade (UK - Normany - Holland)
41 (RM) Cdo
46 (RM) Cdo
47 (RM) Cdo
48 (RM) Cdo
The Brigades were renamed from Special Service Brigades to Commando Brigades in late 44. On demobilisation and disbandment of the Army Commandos, 3 Cdo Bde was retained as an RM formation (presumably because that was the one already based in the Far East).
The Commandos were numbered 1-12 & 14 (Army), 30 (joint service, intelligence), 40 - 48 (RM), 50 - 52 (Army, Middle East) and 62 (Small Scale Raiding Force).
Hence why 3 Cdo Bde remains, and why the RM Cdos are numbered 40, 42 and 45. FPGRM = Commachio Gp = 43 Cdo; I presume the other RM Cdos were disbanded on the basis of their location no longer needing to be garrisoned (41 Cdo - Malta) or on the unluck of the draw!
That is just a very brief summary garnered from Chappell M, Army Commandos 1940 - 45 (Osprey, Oxford, 1996)... more than happy for those who know more to expand / rip to bits!