Thanks for your quick reply! I wouldn't normally be replying until the evening but it's my birthday so I've taken the day off!
I've already had the door panel off, it's the cable that's the problem. It gradually chewed itself up, then snapped. I've already changed the driver's side motor/mechanism twice since I've had the car in about 4 years so have an experience in this field! Ideally, the best thing would be to change the whole lot, because the motor was getting a bit slower before it snapped (probably due to the friction of the cable!).
Should I replace just the cable? Surely it's not that easy to get hold of just a cable, better off with a complete motor/mechanism?