yeah, that's why you can't just walk in and become SAS.
The SBS happen to be known as more bad ass. the navys equivalent to the armys special air service. The Special Boat Service.
They're meant to be more hardcore, you have to have 3 years military experience before applying for either. Both hard as nails.
in the paras over here .. Parachute regiment they do this thing called milling. Which is controlled agression, you hit each other for a minute none stop, you don't block, you don't dodge, you just punch straight at each others face.
YouTube - para milling
there's a vid, I know it just looks like wild swinging, because basically that's what it is. It's not about form but more about who can take the most and not back down.
Anyway, apparently the SAS/SBS do that with no head guards and no gloves, pretty fuckin hardcore.