Meanwhile, British feminists have already missed the chance to find a new kind of modern sexual morality appropriate to the 21st century.
In practice, Anglo-Saxon feminism never liberated itself from the Puritan morality that downplays or rejects all forms of pleasure as sinful.
Meanwhile, Nordic countries are already way ahead of the game.
Couples openly discuss “parallel relationships” within marriage.
Yet marriage is a protected and respected institution in these countries, where families can function and flourish without compromise.
And let’s not ignore the past in drawing up a new 21st‑century road map of adultery.
Just as the Pill opened up premarital sex in the Sixties, the internet is opening up a whole new culture of affairs among married people.
Emperors cavorted with courtesans, kings chose their wives for political manoeuvres and their mistresses for company, the aristocracy married for money and took lovers for pleasure.
Indeed, the conventionality of affairs is displayed in the concept of le cinq à sept, the magical space between 5pm and 7pm when men see their mistresses.
In Japan a tradition of geishas has evolved into a modern society where sex is seen as a pleasure to be enjoyed.
These range from affairs between work colleagues lasting years to holiday flings lasting a few days.
Almost half of Finnish men and almost one third of Finnish women have had at least one significant parallel relationship.