im having the same problem mate. I used an extension lead and my wifes hairdryer. took about 5 minutes blasting in behind each wheel on full heat, keep yanking the handbrake up and down too, being careful not to snap the cable, this cracks the ice in the mechanisms. It does the job but it will freeze up again if you park up. park it in gear and turn the wheel into the kerb with the handbrake off if you need to use the car again in the day.
Northern Irelands having about -10 at the minute. not great for my car and crap handbrake. hope it helps my friend.
Danny
December 2009