I finally found what the problem was.
I remembered an odd problem I had had a while ago when trying to connect into my home Linux system from a Fedora system at work (this was several months ago, in April or even a bit before I think). It took me ages to find the problem that time, I eventually spotted lots of errors in my Speedtouch router's error log saying things like:-
FIREWALL fast tcp seqnr check (1 of 2): Protocol: TCP Src ip: 192.168.1.1 Src port: 22 Dst ip: 193.128.168.194 Dst port: 51097
I just found that my new Fedora 7 installation at home couldn't connect to the configuration web server on the Speedtouch router. ... and in the error log I see just the same errors being reported by the router.
So I have disabled this particular firewall check and now it all works! Hurrah!
(I had lost my previous disabling of this firewall check when I reset the router a few weeks ago)
I'm still not sure whether this is an error in Fedora or an error in the router.