The lock on the fuel cover (body panel) will not unlock?
 
                Citroen Xantia, 1.9TD LX, L Reg
The small body panel that covers the fuel cap has a lock that releases with the central locking.  I can then flip open the small panel and unscrew the fuel cap and refuel.  However, the lock will not unlock.  How can I fix this?
            
             R Kestle
            
 April 2008