She seems rather on edge and sends me a text message at the time we're due to meet asking why I'm using the website.I reply, telling her to come over and ask me face to face. She looks furtively around and asks me if I'm nervous. There is tension in the air like North and South Korea coming together to hammer out a treaty.She wants instant gratification even though we've exchanged only a few words online.

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.

She has declined to tell me her name, so I have to think of her as her web sobriquet.

This is how I find myself waiting for "Sophia Loren".

I'm already starting to feel like I've had enough of this experiment.

But if I'm going to find out what really makes these women tick, I need to leave the safety of the virtual world and see them for myself. I arrange to meet a 41-year-old mother of two who misses "romance and flirting", in a cafe in two days' time.

We have encountered one another via an internet dating service established for the sole purpose of enabling married people to commit adultery.

It may sound like an unpleasant niche website for a handful of amoral people to whom wedding vows never meant very much.

The idea is presumably to safeguard people from searching for their own spouses on the site - though how a husband would explain to his errant wife how he came to stumble across her picture on a website for adulterers, I don't know.

In order to fit in with the general ethos of the website I have invented a wife.

"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.