Been trying to nail this one for years. This is as close as I’ve managed to get so far:

There’s a preponderance of “boy meets girl, ‘sport and play’ ensue, boy promptly deserts girl, girl is left ruined and/or holding the baby” songs in the tradition. It’s odd that they became so popular - via the 60s folk revival - at approximately the same time as the arrival of the pill. I think the libidinal focus in such songs shifts at that moment, from being about enjoyment of transgression followed by moralistic re-assertion of “the consequences”, to being about the emotional pain of deserting or being deserted by other people - a strong theme in the contemporary songs of Anne Briggs, for example. The issue then is not that the girl has “lost her maidenhead”, with all that might once have entailed, but that she’s been cheated in some less palpable sense - although it is not always quite clear who is cheating whom, or what in any case might be owing in such situations. This anxiety is raised so as to serve as a moral counterweight to the rhetoric of naive sexual liberationism, which tended to portray the unshackling of sex from reproductive function as (in Larkin’s words) “a brilliant breaking of the bank, a quite unloseable game”. It is, in other words, a symptom of unease with “freedom”, akin to that expressed by Bert Jansch’s “Needle of Death” which explicitly correlated the damage caused by widespread drug misuse with “man’s desire / to free his mind, release his very soul”, which ultimately confirms only “that death itself is freedom for ever more”.

Addendum - hear it from Anne Briggs, as everyone should: