In system maintenamce > management, I have unticked Allow management from the internet, so I would expect that if I try to access the router via the public IP address, it will fail. In fact this is exactly what happens with http but if I use https, I am taken to the login screen. It does not accept my login but I am wondering if this is the normal and expected behaviour? I would have expected not to be able to go the the login screen at all. I have the latest firmware.

are you possibly getting confused with the SSL VPN login screen?

Ah.. quite possibly, although I didn't know there was such a thing, although I am aware that there is a Smart VPN Client that you can install on a PC and use that to connect to a remote network. So does this SSL VPN login screen work in the same way? Thanks.

The router's SSL VPN service does listen on TCP port 443. This can be set from SSL VPN > General Setup to change the port. To disable SSL VPN, go to VPN And Remote Access > Remote Access Control and disable the SSL VPN Server, it will require a reboot to apply that change.

Thanks everyone. Question answered.