As mentioned, the key fob has not worked for some time.
I use the key, that has no fob. to start the car and up until now operated the central locking from the external lock on the driver's door.
Checked today, and the key, without the fob, will lock the central locking as before. However, it will only unlock the driver's door and not the others.
The problem has nothing to do with a key fob.