It's easy. You pick them up from the shelves and take them through the till. A pharmacist at the till may remind you not to take too many or ask what other medication you're on, but in a supermarket you can just take them straight to the main tills and have them go through with your normal shopping. I imagine even a normal till-worker might balk if you tried to buy several packets at once, but I wouldn't want to bet on it; not the way the one I had today was mostly talking about her ageing labrador's arthritis... The with-codeine variants like Solpadeine are 'behind the counter', at proper pharmacies, so you do actually have to go up and ask for it from someone with a bit of training. But that's it, and if the staff at one pharmacy are starting to recognise you and query your purchases you can always go to another. (It was when a supermarket pharmacist refused to sell me more than a half-pack, and that after a lecture, and I found myself starting to think about going out of my way to other pharmacies to avoid such recognition, that I decided to take it as my wake-up call.)