Right, time for an update.
I've taken the tubbed adhesive back, and Topps own bagged adhesive was the same price as the BAL! So I went round the corner to another shop and I've come away with Ultra Pro RapidPB (wishing I hadn't bought rapid now). I don't know if it's white, but it's definitely cement based. Is this still usable? I did mention that the walls were tanked, but one guy didn't know what it meant, and the other guy suggested it was OK to use any adhesive over tanked. I'm struggling to get good product advice in these shops. I think what I should have done was asked for a shopping list on here first :mad2:
Anyway, back to the tanking. For reference, I'm using the Mapei tanking kit - it was on special in Screwfix at £39.99
Doing the corner strips was pretty easy, and they overlap the bath nicely. One comment is that the instructions say a dry layer thickness of 1-2mm is ideal! So I gave up with the roller and started slathering it on liberally with the brush. I'll leave it an hour or so now and get another layer on.