I stumbled across this Frostwire spin-off application and downloaded it and it connects fine. So whatever was wrong was specific to Limewire. No idea if this will be of any help to anyone as no-one's logged any responses but there you go, take it or leave it, probably worth a try as its a damn site easier than buggering about with firewalls.

FrostWire.com » Official Website & Free Download, BitTorrent «