Terrain warning light Dash terrain light comes on even though we have never been off road, anyone know why?

A bit more information would be useful. E.g. car model year and mileage, any other symptoms (vibrations, other warning lights or messages, etc), when exactly does this light appear (all the time, only on start-up then goes off, etc). The more information you can give us the more likely we are to be able to help.

Such warnings may be caused by a number of things, including problems with the Active On-Demand Coupling (Haldex), so getting any fault codes read could help identify the problem.