This is interesting. UK declaratory judgment action by homeowners against some sort of parks authority, on the question of whether the public had a right of access -- and the court says that it was error not to join the attorney general as a necessary party, as otherwise the general public wouldn't be bound by the decision. (Presumably, if it had gone the other way.)
https://www.thetimes.com/uk/law/article/why-wild-camping-is-not-prohibited-on-dartmoor-6tn7ms2wk