Sorry but it won't work.
You need to have a cable modem given to you from Telewest themselves when you open an account with them.
It will only work for that given address and needs to be officially registered by Telewest.
We keep on telling people time and time again, that modems bought off ebay will not work.
If you have registered for an account with telwest, you will have been supplied with a modem.
to the forums by the way.