How I wish this worked.

Unfortunately, It usually doesn't. When the SAS get into fist fights, its inevitably a pub fight. Pub fights involve weapons - like chairs, bottles, and anything that comes to hand.

Taking on anyone with a firearm when you're unarmed is plainly stupid and will probably end up with you being killed. Only do it if it is a matter of last resort.

The SAS don't train for that much unarmed fighting. This is another myth that surrounds the hallowed Winged Dagger (Actually Excalibur, but who's counting?).

Incidentally, if you want to win an unarmed fight, I'd suggest bags of aggression, and a load of the motto Who Dares, Wins. Oh, and aiming for the throat and the groin might help.