The news throws a huge question mark over the future of Flextech, which has a half share in UKTV, and its sales house IDS. NTL and Telewest, which own Flextech, admitted it was powerless to stop the BBC walking away from the UKTV partnership.
The cable companies' merger has triggered a clause in the UKTV deal, which enables the BBC to buy back Flextech's 50% stake.
It is potentially a huge blow to Flextech, which relies on UKTV for more than half its revenue, and comes just a week after NTL chief executive Simon Duffy said that getting its hands on the content division was a "key part" of the merger.
The chief executive of BBC Worldwide, John Smith, has said he will embark on talks with rival operators, believed to include those who previously bid for the whole of Flextech, including BSkyB, RTL and ITV.
However, sources suggest the BBC may prefer a US partner, with Smith having recently announced that expansion of its international channels, especially BBC America, was at the top of his list of priorities.
Discovery, Viacom and AOL Time Warner are all believed to have bid for Flextech, but Discovery could be the frontrunner as it is just three years into a 10- year partnership with the BBC to develop television channels and factual programming on a global basis.
The broadcasters have worked together on hit shows, including Walking with Dinosaurs, Walking with Beasts and Blue Planet, and have also developed jointly-owned TV channels, including Animal Planet, which already reaches more than 80 millions homes in the US, Latin America, Asia- Pacific and Europe.
Furthermore, Discovery is the marketing and distribution partner and advertising sales house for BBC America, the BBC's wholly-owned entertainment and news cable network.