Hi Bart you have exactly the same symptom as i did.
What actually happens is that beneath all the twentieth century remotes and stuff there is a 1970s wire coat hanger attached to a central locking unit in the bottom of the door which falls off the key barrel.(sorry Richard no micro switches on the barrel all in the bottom of the door) The fix is to bend it more than it already is and place it back in the barrel.
The bad news i couldnt manage it without stripping the door down to its basic parts.
To check if you have exactly the same symptoms insert the key and turn clockwise and anticlockwise you should feel no resistance at all. If this is you then i can detail how to strip out the door but it will be a novel probably better if you pm me.