Ofcom in theory has access to lots of data from providers, and should thus be able to produce statistics easily on what services are available to parts of the UK, and an interesting UK wide figure has emerged. To quote exactly "Customers who are unhappy with their current speed could also consider switching to a faster package or provider, particularly if superfast broadband services are available to them (63% of UK households now have access to superfast broadband )."
Inexplicably the figure was buried in amongst the latest round of mystery shopper research published by the telecoms regulator. On immediate viewing the figure looks far too high, as Openreach superfast coverage has only just reached 38% of the UK, and Virgin Media cable services only cover 48% of UK households. The solution seems to be that there is not a total 1:1 mapping between Openreach and the Virgin Media cable network, which some have accused Openreach of having. The 63% figure is feasible if 15 percentage points of the Openreach FTTC and FTTP coverage are outside Virgin Media areas. The actual figure for Openreach outside Virgin Media areas may be a few percentage points lower due to the presence of alt-nets, e.g. Digital Region has a footprint of around 3% of UK households.
Update 20:30 Added a figure for Digital Region, who provide VDSL2 in South Yorkshire via sub-LLU, though their coverage does overlap some Virgin Media and Openreach FTTC areas too.