Aha. Had a hunch, and remembered that someone said here that broadband problems are the only ones that go through to the Indian call centre. So I chose general enquiries instead (option 5), and a nice scottish woman upgraded me straight away. Ok, so she upgraded me to 1mbit by accident, but phoning back got a nice scottish bloke who fixed it straight away. And I was answered in like 2 minutes! Great stuff from NTL (compared with a year or so ago), just rubbish stuff from NTL when it comes to their cheaparse Indian call centre. Honestly, British companies should be taxed to the hilt for effectively sending money out of the country (like when you try to bring in a purchase from abroad).
So, to sum up, don't worry about having a router plugged in; it makes no difference. If you get an error with the online upgrade then phone up, but make sure you do general enquiries. And you *will* lose any offers. The scottish woman told me I would lose my bought my own modem £20 a month special offer, even though it was a free upgrade. She then asked how long the offer was for and how long I had been on it. I said since the beginning (4 years?), and as far as I knew there wasn't any cut of date mentioned. She then amended my bill to be £25 a month, with a £5 discount. So I effectively kept the special price! Oh yes.
Now to use up my cap on a couple of Java downloads
Cheers