I think I would be right in saying that the NTL connection that you have will require that you register a MAC address for any computer to connect to it and they (NTL) may not like that.
The way around it is to set up your PC and his as a network and to share the internet connection that way, Your PC will in effect be acting as a gateway to the NTL COnnection and therefore you will be using your own MAC address.
Post back with details of your PC (Does it have lan connections/does his laptop?) and also what operating system you have. we will see what we can do.