Unresponsive drivers door handle lock

Hi all, I've got an unresponsive button on the drivers side door handle which locks the car externally. Any ideas on how I go about fixing this? Can the button be replaced or does the entire handle need to be swapped out? If so, I've taken the door card off but cannot for the life of me see how I'm meant to take the door handle off.
 
its a great job fitting new handles on 197/200 lol....proper fiddle if you not done them before!