Response to P. J. Dunn:
The demographic evidence of the birth-rate in the UK is that there wasn't actually a single "baby boom cohort". Search for the official statistics document "The UK population: past, present and future", file-name 01_fopm_population.pdf, and look at figure 1.13 on page 11. (Enlarge it to have a closer look). Here are important facts:
There was what I'll call a "baby-spike" immediately after the war. This 2nd highest birth rate of the 20th century peaked in 1946/7, and lasted very few years. The reason for that spike is obvious. (For example, my parents met during the war and I was born in 1947).
Then there was what I'll call a "baby-peak" 19 years later. This highest birth-rate of the 20th century peaked about 1965, and was much greater and longer-lasting than the 1946/7 baby-spike. In fact, the birth-rate during the baby-peak stayed at least at the 1946/7 baby-spike rate for about 10 years, and arguably (make your own choice from figure 1.13) the baby-peak lasted from about 1959 to 1971. I don't know what caused that baby-peak, but perhaps it was something to do with increasing confidence in the future?
This suggests that there are really 2 relevant cohorts rather than one. The smaller of these cohorts covers births from 1946 to about 1950. The larger, and potentially more important, cohort covers the range from about 1959 to 1971. (But judge for yourself from the graph of figure 1.13). These should probably be thought of as separate generations, although they overlap a bit.