At first, when Bartell infiltrated them, the swingers - perhaps not surprisingly - offered him and his wife the warmest of welcomes. The Bartells, however, had their minds on higher things. Despite meeting more than 400 swingers, they never had sex with any of them. But when, as an experiment, Bartell grew a beard and long hair, the swingers shivered in collective disapproval and shrank away. The message was plain: this time he had really gone too far.

The internet, of course, signalled the biggest change of all. Within the last few years, any stigma attached to advertising for a mate has disappeared. In Britain alone, 26 million people have enrolled in online dating sites. The results, for the traditionalists anyway, have been mixed. One dejected would-be adventurer quoted here bemoans the way in which everything has become like "a sexual McDonald's". No longer do personal columns offer an exciting encounter with the unknown. Now, people stipulate exactly what they want, unencumbered by any fear of embarrassment, or exposure.

And there's a sense too that in the rush towards blatancy, something else has been lost. In classic personal ads one finds the coy and the plaintive sitting squeezed together to strangely beguiling effect - as in this announcement that appeared in Correspondent magazine in 1969: "Torbay area. Sincere couple 38/28 interested in absolutely everything erotic wish to meet others similar for anything goes. Hurry, we are so bored down here and very genuine."