I spent 4 months back in 1975 in the sleepy village of Sutton Bridge, England during a time of revolution in the English beer industry. There were two major changes in the English pubs. One was the introduction of a pilsner tap, usually Carlsberg, seved unrefridgerated like the ales.
The second change was the introduction of “top pressure” in the casks to deliver the ales and beer that previously were drawn from gravity.
These created a problem for the publican who was obligated by law to serve his patrons pints filled to the rim (unlike the Germans who do require a head). To solve this problem larger pints with a white line near the top to indicate a full measure were introduced. That did not satisfy many who demanded the full measure to the rim regardless. The English pub patrons were a stickler for tradition.
I was amused during that time with the lack of expertise in pouring beer and ale.
For example, they poured the pilsner not against the glass but right into the previously poured pilsner resulting in a huge head that they slowly allowed to spill over while filling until full measure was achieved .
All the while I heard much debating regarding the effect of taste due to top pressure. I visited one pub in Long Sutton which did serve gravity fed ale, but I couldn’t tell the difference.
Norwich bitter was my choice at the time. 19p a pint. Most of the men drank bitter in the pubs which was relatively flat but very flavourable. You felt like you were getting nourishment as well as alcohol.