what is to stop BT changing all future FTTP provisions to FTTC and then make more money by charging to upgrade to FTTP. Isn't this just a way to make the BT pot stretch further.
There is nothing whatsoever stopping BT from changing the plans. It's their investment money, and they get to choose how they want to spend it.
In the end, it will come down to choosing the most efficient way to rollout the bandwidth - whatever technology that requires. That alongside one eye on the future.
also why should it be possible that BT can decide to provide FTTP straight off to some EUs but then expect others to pay great costs to get the same result.
Same answer.
In reality, I guess the "area-wide" installation of FTTP will happen for those places where it is more cost-effective to use FTTP than FTTC - or where FTTC isn't suitable. This might be places with more poles, or might be places with sufficient conduits. It cries out as the solution for those on direct exchange lines, and plausibly as an FTTB solution for flats.
However, I think the best way to read the on-demand-FTTP product is that it is really targetted, initially, at businesses and maybe a few early-adopters. It won't be quite right for mass install yet.