Then I suggest you download and read through this PDF document from the Land Registry (I assume you are in England & Wales - different process if you aren't).
http://www1.landregistry.gov.uk/assets/library /documents/lrpg005.pdf
Then ask more questions if you need to.
Don't go and speak to the owner.
This process only works for unregistered land. Since 2003 its been a lot more difficult (nye impossible) to make a successful legal claim registered land.
You may need a solicitor to help you though in theory it should be straightforward.
One issue is likely to be whether the owner has given you consent. If he has ever put it in writing, that constitutes consent (and a claim for Adverse Possession will fail). Not sure what the LR will say about a situation where the owner knows you are on it (illegally) but simply has done nothing about it.
Alternative may be you just buy the land off him if he's friendly and wants little for it.