how can I open passenger door on rover 218 vvc coupe?

The passenger door on my Rover 218 VVC coupe wont open even though the drivers door opens O.K. with the remote, I cant get the door to open even from the inside by manual use of the button. I dont want to destroy the door lining in order to get at the lock as I am afraid that a replacement would be harder to find than rocking horse sh*t, and I need to get it opened and the servo or lock mechanism fixed before the M.O.T. is due in August. I have been told by a Rover specialist that there is a method of disarming the central locking system but for comercial reasons he wont tell me what it involves, can any body out there let me in on the secret.