@Sunshine 

Hi. Thanks you for your response.

I'm not an IT guru so I'm not sure how to tell if it's public or private. I think it is private IP/CGNAT as it is in the range 10.150.xxx.xxx. The DNS servers are in the 82.132.xxx.xxx range, which I believe would be public.

I'm not that bothered about remote administration of the router. That was just a test to see if I could reach the router from the internet.

What I actually want to achieve is a gateway (if that is the correct term) to a non-OS device (a PLC) that sits on the router LAN. Basically, I want to pass all traffic coming in from the internet to this device, preferably only traffic from  a whitelist would be allowed through. Would this be possible with a private IP/CGNAT address?