The Ashley Madison agency, which has 855,000 members in the US and Canada, promises "romantic rendezvous for the attached, " and its founder says he believes there will be a "voracious appetite" in Ireland for the service.

The North's Free Presbyterian church has denounced it as "technological prostitution" and says it poses a huge threat to local marriages.

"Unfortunately, because it's a website, there are no premises for us to picket, " says the Rev David McIlveen, a prominent member of the Rev Ian Paisley's church. "It's a vile, reprehensible site which appeals to baser human instincts. Sadly, I fear many men surfing the net might be lured in. Infidelity could be only a click of the mouse away."

The website's slogan is "When monogamy becomes monotony." Users choose a county and then access a list of other sexually frustrated locals.

Agency founder, Canadian Darren Morgenstern, believes business will thrive in Ireland: "I've heard all about the Emerald Isle, " he told the Sunday Tribune. "In a conservative society with lots of sexual repression, people want to do it more. Most people claim to be anti-adultery and say it's only for riff-raff.

But 70% of husbands and 50% of wives stray and if you count those who want to, or do it in their heads, it's almost 100%.

"Many people are living lives of quiet misery. For financial, social or religious reasons, they don't leave their spouses, but they're unfulfilled. The person you married at 25 mightn't be right for you at 45. It's never usually just about sex. People are looking for someone to connect with."

A total of 85% of the website's users are men but female users are "very committed." Morgenstern denies the clinical nature of the site puts women off. The average user age is 36 and users are from all social, economic and educational backgrounds.

It costs 2 to email another user. Men generally look for more than a one-night stand but still have sex with women they don't find attractive, while women want "a knight in shining armour."

Morgenstern says threequarters of men who have heart attacks during sex are with their mistresses, although he hopes no such problems affect Ashley Madison liaisons. He will be advertising the site "discreetly" in local newspapers and radio stations.

The Rev David McIlveen says he has been married for 33 years and fidelity is vital:

"What type of man makes money from trying to wreck marriages? How does Darren Morgenstern sleep at night? The people behind this site are as responsible for what follows as drug pushers are for drug problems.

The Bible says: 'The day thou stoodst on the other side, thou wert as one of them.' I don't believe local women will use this site. I fear we'll end up with young girls from third world countries and eastern Europe being exploited."

But Morgenstern says McIlveen has an idealistic view of local women's capacity for adultery: "With all due respect to the reverend, he's out of touch with reality, and he's confusing prostitution with infidelity. Our members are real people with genuine circumstances. Adultery is not illegal. A website doesn't cause infidelity. Most affairs usually start in the workplace anyway. We don't encourage cheating, we just offer a business service.

"People logging onto our site know what they're doing.

Many find us through Google and other search engines.

People use credit cards, hotels and mobile phones to have affairs. Are those businesses to blame for adultery?"

Morgenstern (42) is married to a 27-year old: "I haven't cheated on her and don't imagine I ever would. Being a fly-on-the-wall to infidelity helps you do what's necessary to have a healthy relationship." It's his second marriage, so did he cheat on his first wife? "According to her or according to me?" he says, and laughs.