My remark was sort of based on Ofcom's WFTMR statement for 2021-6, particularly volume 3, available from
here.
I'm no expert, and I'm not going to go into all the all the details here (vol 3 alone is over 200 pages). Read the referenced docs for more info. But section 2 of vol 3 defines a procedure for withdrawing copper regulation **where and only where full fibre is available**. Where it is not, there is no change to existing WLA regulation.
The WFTMR defines two thresholds:
1) When 75% of an exchange area has FTTP available, a copper stop-sell can be introduced;
2) When an exchange area is "complete" (all properties connected, with exceptions essentially where it is logistically or legally impossible to connect) then price controls on copper products are relaxed.
Presumably copper prices will then rise sharply to encourage remaining customers to migrate. This scheme was deliberately designed to incentivise OR to complete areas, rather than just do enough of the easy bits to discourage competitors from building, and then never complete the harder bits.
The 2020 consultation docs which preceded this WFTMR contained a proposed third threshold for the complete deregulation of copper services (ie allowing them to be withdrawn completely). This was not included in the WFTMR, because it was thought unlikely that any exchanges (apart from Salisbury and Mildenhall) would complete the first and second stages by 2026. Thus I don't think there is any Ofcom defined mechanism for copper services switch-off before 2026. Something along the lines of threshold 3 will almost certainly be part of the WFTMR for 2026 onwards, but unless it is radically changed it will be predicated on the availability of full fibre.
Some of the comments above seem inconsistent with the current Ofcom regulatory framework. That of course can and probably will change over time. Maybe some contributors are predicting how things will work out in the long term, rather than how it will be for the next 3 years or so?