Central locking key not working for Renault Clio?

I have just bought a second hand Renault Clio, and the central locking was working fine but now it's stopped. The light is occassionally turning on. Have checked the batteries and they are not flat. The key works for the boot, passenger door and in the ignition, but will not lock or unlock the drivers door. Is there anyway to disable the central locking completely and just use the key manually all the time?