Rover 45 central locking?

During the cold weather I have not been locking the car with the key fob or key to try and prevent the door / central locking freezing however the other day after driving 10 miles and stopping to get out the drivers door would not open so I had to climb out the back . The knob on the door latch does not operate fully up and down with either the key or the key fob however all the other doors do - have had the car in my garage to thaw out for 2 nights and still no better - thought this door lock might have frozen