https://www.bt.com/broadband/availability/ still only offers the packages I showed earlier.
However, https://www.bt.com/broadband/deals says "Great news - You could be doing more online with Full Fibre 900" - with my address - and *does* show all the products up to 900. (But oddly, not the 80/20 package).
Well whaddya know: today https://www.bt.com/broadband/deals offers me Fibre Essential (FTTC), Fibre 1 (50/10) and Fibre 2 (74/20), but *not* the higher speeds any more.
Looks like they are having problems building a reliable and consistent availability checker.