Service personnel serving overseas are only subject to UK criminal laws by virtue of the fact such laws are incorporated into the service discipline acts (eg AFA 1955).
Or because we are bound by UK Civil law (which has primacy?) when representing HM Government overseas. Just to add to the confusion, what about those situations where personnel are serving in places where the local law is stricter than the UK law (e.g. blood alcohol limits for driving in Germany). How would this affect the situation? In order to keep in with the thread, does this sort of thing apply to your flying regs, and what happens if you 'accidentally' break them?