Following on from this. I had a brief chat with my local dealer this morning and they have done some servicing work on SA hardbodys before and the rep there said that he would need make/model details plus chassis number to see if they could obtain the key then it will all depend if they can obtain the programming code for the immobiliser/alarm and you would need to take it to the dealer to get it checked. That's £40 just to check it out.
My local Nissan (Hammonds, Halesworth, Suffolk) are really helpful and will do what they can to help. Try them on 01986 834730 even if it's just to pick their brains.