Hi, Thank you for the quick response. There is only one router, so the address you quoted is the WAN address.
Unfortunately, what follows will probably be of no help to anyone with a similar problem, as I am not sure which action solved the problem.
While doing general maintenance of my PC, I purged all unnecessary files, cleaned and compressed the registry and ran chkdsk. On reboot I was greeted with the dreaded blue screen. Booting into safe mode met with the same outcome, but last known good rescued the situation.
Now BitComet immediately opens the listening port. I'll probably never know what was causing the problem.
Once again thank you for you assistance.