...and spoke too soon as now it's stopped working again
I've set up port forwarding manually AND port 4040 shows up on the list in UPNP settings on the router but can't reach the host and my subsonic.org address is showing up (NoRouteToHostException). Unticking autosetup in Subsonic so it just uses the manual version doesn't work. Ticking it again brings up the UPNP port on that setting page.
Further efforts added:-
I've deleted port forwarding manually and let Subsonci open port 4040, which now shows up on the list in UPNP settings on the router but can't reach the host and my subsonic.org address is showing up (NoRouteToHostException)
Came back to it after some lunch and port 4040 was blocked again... Messed around in the router UPnP settings without actually changeing anything and port 4040 came back on stream!
I'm using
http://canyouseeme.org/ so I'm not suffering loopback in trying to check the port from within the LAN. I'm also using portforward.com to try and set it up, which says you need port 80 and port 4040 open to make Subsonic work. I can't get port 80 to ping though.