I should have elaborated a bit tosh, yes they are still responsible for H&S, and do have policies etc in place, but in many cases by law they are exempt, take driving for example, the forces have a drivers hours policy that roughly is the same as the civil regulations, but when you check civil regs, it simply states armed forces/ fire services etc exempt, there are other trades exempt as well, take HGV mechanics for example, do not require CPC training to drive HGV
there is other areas as well, transport of ammunition and explosives is one of the top of my head, they are totally exempt all Uk regulations, but in practise they are more rigorously enforced than any civilian company