They are allowed to sign up for free as a way of ensuring the numbers are balanced between the sexes.
I register, and enter the murky world of two-timing technology, taking note of the warning on the site: "Not all affairs have a positive effect on a marriage." What a masterpiece of understatement.
Reading it on my laptop in the aptly named Cafe Affaire in central London, I consider what she really wants: a no-strings-attached sexual relationship.
What I don't know is how her husband will feel about it. Aside from the little matter of her marital status, she also believes I have a wife, but she doesn't care.
"My preference is for a man who is much younger than me with rugged features," says one. This is a way of paying someone a compliment without typing out the words. And over the course of a week I get almost 100 replies, messages and propositions.