For reasons of promoting competition BT was shut out of cable provision for years. When it became clear that the competitive situation wasn't going to deliver anything like a nationwide service once the cherry-picking was done BT was allowed in and started the much bigger investment of building a much wider FTTC network. Being an experienced telecoms company they laid capacity for expansion; much of the cost is in all the field operations so including the spare capacity now is a relatively small investment compared to what it would cost to do it later.
I remember reading an article (god knows where but it was years ago) which stated that BT were in a position to offer CATV. To be able to do so they would need to speed up the deployment of Broadband nationwide which was seen as the real prize. The article said that the regulator was dragging heels and whilst the cable companies were never going to extend their cables into rural Britain BT probably would.
Biting the hand that feeds IT
