First the best thing to find out is whether the land is registered or not. If you've spoken to the Land Registry then they may be able to confirm either way for you or you can send off an index map search with a plan with the area marked...
http://www.landregistry.gov.uk/assets/library/ documents/sim.doc
These are free for the first 20 titles and extremely unlikely that it will be any more than that. Any queries about the form let me know.
If you let me know where the property is I can tell you the appropriate land registry to send it to if you're not sure.
Trying to obtain adverse possession differs depending on whether the land is registered or unregistered.
These are the LR practice guides, more for practioners...
Registered
http://www.landregistry.gov.uk/assets/library/ documents/lrpg004.pdf
Unregistered
http://www.landregistry.gov.uk/assets/library/ documents/lrpg004.pdf
These will give you an idea of what you will need to prove and information which would be needed in any supporting statutory declaration (declaration of facts supporting your application which is sworn in from of a solicitor etc...and is a criminal offence to swear a false stat dec).
If you come back with some more info I can help you try and structure this if needs be, not the info itself but how to set it out and the kind of things to include etc...