A third of divorces in the UK have apparently been triggered by flirting on the social networking site Facebook, according to a survey carried out by divorce website Divorce-Online.

While in December 2009 20% of behaviour petitions cited ‘Facebook’ as a reason for filing divorces, the social networking site has been cited by 33% of people as a cause of their relationship breakup in behaviour petitions in 2011.

According to the website, the three most common reasons where Facebook figured in the allegations were inappropriate messages to members of the opposite sex; separated spouses posting comments about each other; and Facebook friends reporting spouse’s behaviour.

Mark Keenan, spokesman for Divorce-Online, said social networking has become the primary tool for communicating with friends and is taking over from text and e-mail in her opinion.

"If someone wants to have an affair or flirt with the opposite sex then the easiest place to do it. People need to be careful what they put on Facebook as the courts are now seeing a lot more evidence being introduced from people’s walls and posts in disputes over finances and children," said Keenan.

However, the micro-blogging site Twitter was mentioned only in 20 of the 5,000 petitions surveyed, the divorce firm reported.