This has been happening to me quite frequently since about November. I'm getting it booked in to Sturgess in Leicester (I've had enough of Motorvogue in Northampton). I'll keep you updated as to what the outcome is.
Well, I've been to the garage and I thought I should share the knowledge with you. It turns out that after they inspected the computer it turned out that the movement/motion sensor inside the car was faulty and had to be replaced!