...if you going to be caught with a metal detector you can face charges.
That seems a little harsh, eh? A few years ago WWII-era military burials were being dug to find such weapons, I'd guess that's part of the reason for such a law. Thanks vannrox.
Desecration of graves is a big part of such business they don’t like to say about. Nobody abandons such stuff for no reason. It usually involved killing the owners and often on mass scale.
Another reason is a great number of ‘archeologists’ and their families get killed or miamed handling stuff like grenades or trying to use guns which are often in poor condition.
Also near the peatbogs you can find guns in near mint condition and these are prized items for the organized crime. Gangsters paying big money for the weapons they know the forensics would never be able to track back to them.