The cable company has already clashed with Sky this week by dropping Sky News in certain areas where it is not contractually obliged to take the service, and replacing it with the BBC's forthcoming 24-hour news service.
The National Geographic Channel replaced Sky 2, an entertainment channel, and is a 50/50 joint venture between BSkyB and National Geographic TV. Cable operators had expressed concern at Sky 2's ratings, and the decision to substitute it with National Geographic was not a surprise.
A Telewest spokesman would not comment about National Geographic, which starts broadcasting on Monday, but he said: "You ignore what the customer wants at your peril".
Cable companies have complained that Sky forced cable subscribers to take a range of channels they did not want. Telewest has supported the notion that customers should be able to pick and choose which channels they want to pay for.