And BT were prevented by Oftel all those years ago from putting fibre in the ground to give Mercury a chance to expand.
That's what happens when you privatise something that doesn't meet the rules normally required to make a privatisation work: the existence of a market.
You end up applying a series of sticking plasters through regulation which, in the end, helps nobody. This continues to this day. A few Conservative ministers did quite well out of the privatisation though IIRC.
BT is hardly what you would call a proper "privatised company" since it has a Crown guarantee on its pensions. If it were to fail, we all pay.
So the other 50% of the country isn't attractive to Virgin? What about the current 50% weren't BT there with their ducts then?
The cable network was built for TV services, something which BT's network couldn't offer and thanks to the lack of investment over the years, cannot compete with - this is going to be one of the blocks in getting people to migrate away from VM cable to BT's FTTC service - slower top speeds for those who want them, and a complete lack of a comparable TV service. The only area in which BT have the edge at the moment that I can see is upload speeds and not by any huge margin which forms a key selling point.
It just so happens that "cable" was a FTTC service which now happens to be able to support superfast broadband speeds. Whether that's down to luck or forward planning I don't know.