[Pierre]

The U.K. had two national telecoms companies. Within the U.K. it was BT, and in the Empire and overseas territories it was Cable & Wireless (after various incarnations).

C&W formed a subsidiary in the U.K. called Mercury Communications and they built a national Core fibre Network. (using white duct instead of grey).

It was Mercury that merged with all the CATV franchises Hugh listed to form CWC.

It’s evolution was broadly similar to NTL, whereas it was NTL that had the National Core Network and that was bought/merged with CableTel, Diamond, Comtel, Comcast, Telecential ( no doubt a few others, to form NTL)

Telewest evolved a bit differently as they never bought a company that had a National backbone.

They built a national backbone for a company called 360 Networks, but they went bust, and Telewest were left with it.