Plusnet are on the list of ISPs known to block or filter p2p, check out the link below. If you use the forum search to look for Plusnet, you'll find more info!
http://www.gnutellaforums.com/showth...threadid=33712

You could try changing to a higher port (even though the test worked for 6346). Try one in the range of 49152 - 65535. You'll need to change LW's listening port, ports allowed within your software firewall & any ports forwarded through your router.