Ok, looked into it a little more, and it makes me even more angry. It's a city-by-city thing. You can look at the "poster" for the city of Winchester in the link that Suki provided. It's basically just tiny mugshots of 24 people in that city that are prohibited from buying booze.
I still don't get why it's THE CLERK's responsibility to make sure that they don't sell to them, based on some ragged mug shots? And if they make a mistake, the clerk gets charged with a crime? Complete BS!
Ugh, I need to go to bed, this is madness.