I managed to locate the problem. The relay in the central locking box located in the drivers door could be heard clicking when trying to lock the doors, but nothing happened. Opening the box revealed that there are two relays - one for locking and the other for opening (I think). As a test I swapped the two relays and soldered them back on. The locking and opening works fine now. It could have been dry joints?? - anyways I am happy.