The law relating to adverse possession changed substantially when the Land Registration Act came into force on 13 October 2003. For the first important case on the new provisions see LRA and adverse possession.
However, the concept of "adverse possession" has continued into the new system; and there are still many cases where all the old law will apply. The leading case and the starting point when considering the definition of "adverse possession" is JA Pye v Graham (Oxford) Ltd v Graham [2002] UKHL 30. A full explanation of the decision is to be found here.
Various matters relating to adverse possession can also be found on the other pages in this section of the site - see the contents column on the left.