There is a catch - the lower price is only applicable to subscribers who also use Telewest's cable TV or cable telephone service.
blueyonder is a cable-based always-on Internet connection that offers a ten-fold download-speed increase, and five-fold upload-speed boost, compared to 56K modems.
The service is available to four million homes in the UK. Telewest plans to extend its franchises into the south west, following its acquisition of Eurobell's cable operations there.
BT's USB-based ADSL service costs £40 per month. Gavin Patterson, commercial director of Internet and telephony at Telewest, said: “Telewest established itself as a broadband leader when we launched the UK’s first widely available consumer broadband service last year."
The company now has more than 21,000 broadband customers on its network, and also has over 310,000 dial-up Internet customers.