Byline: SAM GREENHILL
SAS troops are involved in the major assault in Pakistan targeting Osama Bin Laden and his deputy, it emerged last night.
They are guarding the mountains between Pakistan and Afghanistan, close to where 7,000 Pakistani forces are locked in a ferocious battle with 400 Al Qaeda and Taliban militants.
Two SAS sabre squadrons - about 140 men - are lined up along the border to prevent the fanatics escaping the onslaught by fleeing into Afghanistan.
Thousands of Pakistani reinforcements yesterday poured into the area where Al Qaeda followers are believed to be protecting Bin Laden's deputy, terror godfather Ayman al Zawahri.…