SAS - The Special Air Service, most famed of the British special forces. Serious fucking badasses.
Paratroopers - an elite division of the British Army specialising in parachuting into combat zones, hence the name. Often the first ones into a fight. One of the three/four (one division is a territorial army division, or some such, which I believe means they stay on British soil and dont deploy abroad) divisions is part of the SFSG, the Special Forces Support Group, and work closely with the SAS on many operations.