Fixed I think, although I don't really understand why.
Having fiddled with all manner of things, and tried some of the suggestions, I rang TeleDanmark and asked them if they were blocking the inbound ports, the said no. So I told them what the problem was and they asked me about the router settings.
The "Ah, wait a minute" came when I told them about the fixed IP address. Then came, "when we say a fixed IP address, we actually mean a non-dynamic dynamic IP address, set the router to DHCP WAN side and it'll work". So I did and it did.
I have all the paperwork out, (because I was trying to fix this), it says "you've ordered a fixed IP", "here is your fixed IP", "thankyou for ordering a fixed IP", "have fun with your fixed IP", "tell your friends about having a fixed IP", but in actual fact they have delivered a non-dynamic dynamic IP. Ho-hum.
