Barry Davis is ex regiment and his books are truth as far as they go unlike a lot of regiment memoirs out there by ex members who have rewritten events to portray themselves in a more favourable light.
SBS are responsible for maritime anti terrorist operations and special operations such as beach recce etc for 3 Commando Brigade. More recently they have had the lead role as special ops in Afghanistan while the SAS have been lead in Iraq.
Other than that not a lot is know about any operations conducted by either for obvious reasons, and if you did know we'd have to shoot you
