"In 1964, preparations began to raise the school leaving age to 16. These were delayed in 1968, and eventually the decision was taken in 1971 that the new upper age limit be enforced from 1 September 1972 onwards"
Clarifying the effect of the implementation date of 1st September 1972; pupils who could otherwise finish their compulsory education aged 15 as at mid/summer 1973, were forced to stay on in education an extra year.