Thanks Roseway but unfortunately that hasn't worked for me.
I have cleared the ROMD (which got rid of the John Lewis default account settings), reloaded V15 firmware from the Zyxel site and then pin-hole reset.
I still can't login as Supervisor and still have options missing (no VOIP or TR064/069 menus to name two).
As I said in previous post the credential for superuser do not seems to be reset via the factory reset procedure.
You can try to hack the config file in order to enable some menu items you do not actually see.
Save you config via the backup procedure in the GUI of your router then open the .conf file and search the string "<Name>Administrator</Name>". You should see immediately over a <Privilege> key in xml format. I copy paste mine, where all the menu items should be enabled. Try to replace yours with mine, I did this way in order to enabled some features that was disabled since I lost my superuser access on an old router and it worked.
I do not see any danger in trying this, configuration can always be reset via the factory restore, but please do it on your own responsibility