Before I disappear down the rabbit hole of the internet in trying to find specific information, does anyone know of any permit type restrictions on using a metal detector on my own land?
I appreciate difficulties with other land and/or when you find stuff and declaring it, but purely using it on my patch?

I think there are clubs around, you could try searching for them or the actual rules - normas para la detección de metales en españa as it seems there might be different rules for different regions. I guess you could also call the mayor or the local police.

Thanks for the ideas. I've seen there is quite some information to wade through but I'm sure I'll get to what I'm after.

Depends where in Spain you are but the following is true.

Historical Heritage Law 16, dated June 25th, 1985, basically states that anything under the ground belongs to Spain. And the discovery—either intentional or by accident—of any valuable object must be handed over to the authorities for study. Once a proper value is assessed, the state will pay out half that value to be shared equally among the property owner and discoverers.

Round here (Altea, Albir) you need a permit even if working your own land, and as the above says. You are supposed to report any and all finds (not that people do).
There is a bloke who goes over the beach (well pebbles) in Albir and he says the local police dont know the law. He tends to find keys and the odd coin. He hands stuff into the local plod if he thinks it might belong (not the jewellery though)

Also the soil makeup here is different to the Uk (if thats where your detector came from). There is lots of aluminium in this part of spain and it affects the signal (the bloke on the beach and I have had a few conversations over the odd coffee or two)

Ahh, right. Interesting info.
My bit of land is in Andalusia and it'd be a bit of a bugger if I have to go through getting a permit or whatever just for that. I don't intend currently going elsewhere.