The social networking site, which connects old friends and allows users to make new ones online, is being blamed for an increasing number of marital breakdowns.

Divorce lawyers claim the explosion in the popularity of websites such as Facebook and MySpace is tempting to people to cheat on their partners. Suspicious spouses have also used the websites to find evidence of flirting and even affairs which have led to divorce.

One law firm, which specialises in divorce, claimed almost one in five petitions they processed cited Facebook.

Mark Keenan, Managing Director of Divorce-Online said: “I had heard from my staff that there were a lot of people saying they had found out things about their partners on Facebook and I decided to see how prevalent it was I was really surprised to see 20 per cent of all the petitions containing references to Facebook. The most common reason seemed to be people having inappropriate sexual chats with people they were not supposed to.”

Flirty emails and messages found on Facebook pages are increasingly being cited as evidence of unreasonable behaviour.