Breaking up is never easy
When the wholesale arm of a company sells a service that is consumed by the retail arm and its competitors, there's a disincentive to price the service competitively, because the losses of the retail arm are recouped by the wholesale arm, while the competition (and new entrants in particular) are priced out.
So BT should be broken up. Without the disincentive, Openreach will push its service to as many takers as it can, to maximise its ROI, while BT Retail will have to compete on price and customer service, instead of having relying on holding a virtual monopoly.
And Sky should be broken up for the same reason. It has a long track record of using exclusive content to attract punters to its platform, or overcharging other platform operators to show its channels. Split Sky into a content arm and a platform arm, and the content will be pushed to the widest possible audience, while the platform arm will have to innovate to differentiate itself from BT and VM.