Since the UK charts began in 1952, which year of the 20th century saw the greatest number of acts who only ever had one top ten hit, if collaborations like Queen + Five whose named parts have had hits don't count as separate acts?

top40weekly.com lists every one-hit wonder in the USA, in chronological order from 1955 to 2016 and the highest position reached. No luck finding an equivalent list for the UK.
https://top40weekly.com/all-one-hit-wonders

chartwatchuk lists every one hit wonder which reached No. 1, in chronological order. It doesn't list every one-hit wonder like top40weekly (which would give the answer to your question, by excluding those who reached #11 or lower).
http://chartwatchuk.blogspot.com/p/list-of-one-hit-wonders.html