Sorry, meant to answer that and forgot.
Exploring. Looking for stuff

Mineshafts, adits. Holes in the ground. Clearing the brambles helps make it easier not to fall in one (they aren't all made safe, even today). I did say it was on old, abandoned waste ground. Well this land is often unusable for anything else. Nothing will grow on it, no houses can be built on it, it's often hemmed in by streams or roads or fields.
It is left overgrown although in some cases the council keep some of these sites maintained to some degree. Normally only if there's an engine house tho. Otherwise, where there are no old buildings to conserve, these areas are just abandoned and forgotten.
Technically they must belong to someone, and that someone is not me, for sure. But who is really going to be interested enough in such places to get upset about the loss of a few brambles?
Answer: there are some people who can get upset about anything