They've changed the laws regarding squatting, so you now can't claim seemingly abandoned property - it always belongs to someone. The Land Registry will have details of all land that's been bought / sold since about 1968 I think. Even if it's not on there it's still someone's land, and if you squat you could be liable for civil or criminal prosecution.
Land where someone has died without leaving a Will either goes to the administrator of their intastacy (usually next of kin), or if no-one can be found it reverts to the Crown (not the Government), and her Maj has it auctioned off.