Agricultural land for sale - as the name suggests is land used for agriculture as a business. Increasingly, farm land is becoming redundant with the decline of farming in the UK, agricultural land is often sold off cheaply. While the land will have no planning permission, you may apply for planning permission for a change of use of the land. Housing pressure in the South East is high, so well positioned farm land may provide an investment or future building plot.
NB. Buy agricultural land wisely - if it is not near to existing housing it may be unlikely to gain planning permission.