You don't even have to leave London to see a night and day difference. I currently live in a new-build flat and have multiple choices for fibre (Hyperoptic are great). I am hopefully soon to be moving less than a mile down the road into a house where my choice is either an offensively slow BT-backed service or an offensively unreliable (so I have heard) Virgin Media service.
If you have a new-build flat in a major UK city you probably have a similar decent choice but the rest of the housing stock (the majority by far) is stuck with BT/Virgin.