Not a lot there mate doubt anyone would say anything to you anyway and all they can do is ask you to leave if they do own it. You could just say your wife/GF lost her ring and you were looking for it,.
I see no problem about metal detecting around the camp. It's not a religious site or a burial ground. As Night Crawler says all they can do is ask you to leave. Maybe you'll find some Italian coins or tin mugs.
As most of the Italian POW's were absorbed into the UK agricultural scene; one mostly finds English eating and cooking utensils. These Italian camps did not follow the workings governing the POW camps used for German POW's. The Italian camps just provided canteen and dormitory facilities - rarely full lock up on a 24 hour basis and were staffed by the Home Guard I think in many cases.
There was also a German camp around the area as well because there were a few who did not go back and married local girls. One I know used to love dancing and was at the Hospital dances where my mum worked as she mentioned he was always there.