BPSS is pretty painless I think you just fill out an online form, SC is more onerous as you’ll need to list all your addresses for the last 10 years (I think) and your finances, and some info on parents and siblings for you and your spouse
again not difficult but tedious. In my case my employer helped out as they had done it before (many times) and Amazon deliveries are a good record of past addresses with post codes.
Ian