It has been confirmed that the armies in Modern Warfare 2 will be:
*U.S.A Army Rangers (Frontline Forces)
*Task Force 141 (International Spec Ops Teams)
*Russian Spetsnaz (Spec Ops) [separatists regiment]
*Brazilian Opfor (Opposing Force - Ultra-nationalists)
The factions from Call of Duty 4: Modern Warfare were:
*U.S.A Force Recon (Frontline Forces)
*British SAS (Spec Ops)
*Russian Spetsnaz (Spec Ops) [separatists regiment]
*Middle Easter Opfor (Opposing Force - Ultra-nationalists)
Sounds great, as long as it has the gore of WaW (Major selling point for me) and I get to shoot things I feel fine. I look forward to fighting with Captain MacTavish and Sniping some terrorists.
So, no chance of the British SAS making their way into Modern Warfare 2? Well, they are like ninjas, maybe they are in there but you don't know about it. I bet Infinity Ward don't know either...