It's something that went on until the 1970s but has largely gone.
However, saying that, I used to work in one of the best real ale pubs in the city and it went on. Cutstomers were not aware, generally, however, some could tell with taste, etc.
I was instructed to filter back myself, and hair, fruit flies and wasps amongst other things were left on the filter paper. DISGUSTING.
DB.