Yes they own the land, bought at a cheap price due to it being green belt which is for grazing or farming only.
That's why the local authority had to make a stand on this one, imagine being able to buy a nice green field on the country and then plonking a mobile home on it. Everybody would be doing it, you be looking over the English countryside with mobile homes scattered across it. Then the foreigners would have there angle on it and before you know it the country will look like a shot hole.