Range Rover P38 4.6 Rear Passenger door won't open from the outside

Hello! Wonder if anyone can help me? I bought this Range Rover a couple of months ago with this problem but need the door to open fron the outside for the up and coming MOT Test. The alarm system has been bypassed and the Range Rover will only lock and unlock using the key in the drivers lock. It is no big problem and the car works fine apart from the drivers side rear passenger door will not open from the outside, the door opens fine from the inside, anyone have any idea what it could be, been told that there is a cable or something that might have come lose, I am disabled and can do some jobs myself but nothing major, is it a case of removing the door card and replacing a cable or more? Any help would be great.