Telewest give out stand alone cable modems in all engineer-installed situations, usually either Motorola Surfboard 4100/5100 or SciAtl Webstar modems. (The Motorola ones are the best, BTW

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They do, or used to do, a service called "Self-Install" where, if you have had an STB already installed, they will activate broadband (up to 1MB I belive) and leave you to connect your computer to the Ethernet connection on the back of the STB. They would also offer a wireless tranciever kit in case using a cable wasn't feasible.