Speedtouch routers: Ridiculous things.
You may find that, even with ports forwarded, it still doesn't work. I have a BT Home Hub and when I forward the ports it doesn't work. I have to put myself in the DMZ for it to allow me to connect/host games.
I know this system isn't using Quazal for its netcode like previous GPG games, but try also forwarding port 61262 as well.