After parking my car one evening I found that the electric handbrake had seized on and wouldn't release. The motor had stopped working so the calliper was locked stopping the rear wheel from moving.
The motor can be removed from the calliper and the calliper turned manually with a M8 spline tool to allow the brakes to be released and the car to be driven. I replaced the motor for £10 rather than spending £220 on a new calliper. After 3 months it's still working ok!