macleod-digger, keep in mind, that for a place to be legal to metal detect in, doesn't mean there has to be an express specific allowance. Eg.: a sign saying "metal detecting allowed here", or whatever. Therefore the LACK of a prohibition, means it's therefore not dis-allowed. To determine if there's a rule or law (if you're skittish), you can do as loco-digger says, and look up the rules for yourself.
Naturally a busy-body could try to say you're running afoul of "disturb" and "alter" type verbage (because maybe they think you're about to leave a hole). The best tactic for this type thing, is to avoid those type individuals, and pick low traffic times. You're simply never going to get "red carpets rolled out for you" by every last gardener or nosy-parker. So since we're in a hobby with some connotations, just use a little discretion (even in the absence of a specific 'no detecting') rule, so as not to ruffle feathers. Ie.: don't do highly manicured lawns when the lawn-mower guy is right there. Avoid *obvious* historic sensitive monuments (when an archie is standing right there), etc....
