this could be a number of things, from underinflated tyres to a bent chassis. The first thing that springs to mind is the steering rack. I think they cost about £40 and then you will need your tracking set at a garage.
If you took your cat into somewhere like kwikfit, i'm sure they would have a look and give you advice for free.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.