Slightly wobbly steering

[Nasta]

The car has a slight problem with the steering, in as much that there seems to be a bit of free play around the centre point. When driving on a flat, smooth piece of tarmac, there is no problem, and the steering feels okay. However, when going across really lumpy/cambered roads, the car veers to one side.

Strangley, when it veers, the steering wheel stays in the same place, but doesnt weight up. Does this signal the end of the steering gear, or could it be down to bd suspension??