I don't think even BT know how much aluminium is in the local loop, there is no data available to show the exact number of lines.
But its possible to guesstimate as has been done earlier in this thread and its likely to be a small %.
FTTH is simply the wisest choice for the future. Significantly more reliable, significantly faster, easily upgradable compared to G.fast (by switching the terminating equipment) and not subject to distance, the weather, or RF interference.
And significantly more expensive and much much slower to deploy..
There is a reason FTTP is being rolled out to a large % of the population in many countries instead of G.fast.
Of course BT prefer G.Fast - simply because they get to re-use their rusty old local loop, which is a major asset to them.
As do a number of other telcos - I think you will find that FTTP is not being deployed as widely as you seem to think [and keep stating] overseas on a commercial basis. Most of what there is was planned well before alternatives such as G.Fast came to light.. and a fair bit will be things like FTTB due to population density which isn't really FTTP (depending on how you define it)
In Germany for instance, Deutsche Telekom largely decided to abandon its FTTP plans in 2012 and go for vectored DSL instead. I think now, they may even have scalled back their plans for G.Fast and are looking at VPlus instead
Even BT wanted to fibre up the country in the 1980/90s as at that point it was the logical option for them - now the business case won't be as strong partly as the alternatives are better.
In the UK, still to this day, a new housing estate gets wired up with copper telephone cables as it's broadband access method of choice. Only if a developer is wealthy enough to jump through hoops does it stand a chance of getting a FTTH development. Completely pathetic in 2016.
It should be a law that every new house has full FTTP provided, and that no new copper local loop is allowed to be built.
The issue with new housing estates is not really down to Openreach even though they seem to be the ones largely expected to fix it. The problem is due to:
a) councils not insisting on decent connectivity as a condition of approving planning permission;
b) not enough purchasers not demanding it from developers when moving in;
c) developers not under any pressure from a) or b) to provide it nor requesting it from Openreach when planning their build (or they just don't tell Openreach/Virgin Media about their development at all until its virtually complete)
I would like to see more a) and b) - then c) would happen naturally..