The threat comes in the form of the telecoms quad-play - broadband/mobile/TV/Internet
In 2014, Ofcom gives BT a estimated market share of 31% of broadband and EE say they have a 33% market share. BT's relationship with OpenReach helps for providing backhaul bandwidth to mobile towers and BT are starting to invest more in TV to improve content provision.
This is largely theoretical, but any precedent set allowing BT/EE will likely be countered by the two main competitors in triple/quad play: Vodafone and Sky
Now for pure speculation:
If it does go ahead, I would expect Vodafone take Virgin and Sky to take O2/3 leaving anyone outside these large players (virtual MNO's, ITV, BBC) in an uncomfortable place.
As for consumers? They will probably benefit from more content (whether they want it or not) but it will come at a higher cost.