Road Traffic Act 1988 section 34
(1)Subject to the provisions of this section, if without lawful authority a person drives a mechanically propelled vehicle—.
(a)on to or upon any common land, moorland or land of any other description, not being land forming part of a road, or.
(b)on any road being a footpath, bridleway or restricted byway,.
he is guilty of an offence.
(2)For the purposes of subsection (1)(b) above, a way shown in a definitive map and statement as a footpath, bridleway or restricted byway is, without prejudice to section 56(1) of the M1Wildlife and Countryside Act 1981, to be taken to be a way of the kind shown, unless (subject to section 34A of this Act) the contrary is proved..
(3)It is not an offence under this section to drive a mechanically propelled vehicle on any land within fifteen yards of a road, for parking purposes.
NB You can drive onto such land to fight fire or save life or similar emergency