You're doing the right things. In the UK there are only three alternatives as far as I know.
The Land Registry, which charges a fee, or a service which uses the Land Registry database, which will usually charge a bigger fee.
The local council but only if the land is owned by the council. I do not know if they charge fees but I'd be slightly surprised if they didn't.
Stand somewhere near the property and shout, ask the neighbours, etc.
About one third of land in the UK is not registered so for private land your chances are only average at the best of times. If it's council owned you would probably need some kind of a miracle to get permission to camp there.
Usually, if you camp somewhere without asking permission, either the owner will be along fairly smartly to tell you to move on or he'll never know unless you leave a mess. Years ago when I was camping in hills in the Lake District, after a couple of days the owner came along and grumbled about the damage I'd done to the turf with my fire. When I pointed to the turf safely taken up so that I could replace it when I left she looked very surprised and said I could stay as long as I wanted.
Once I found four lads in a caravan on woodland that I owned. They were there without permission, doing drugs and an unbelievable amount of wanton damage. I called the police before they knew I was there. One of them had a motor-bike, somehow he, er, managed to fall into a dyke

, and then they all ran off - without the bike. A policeman arrived half an hour later and thought it was hugely amusing that someone had just reported his motor-bike stolen by a wild man in the woods. If they'd been responsible and sensible I'd have been more than happy to let them use the land, they could have helped me to look after it and got something out of it themselves.