Married couples flocking to the Tuscan countryside or the Eternal City this summer might want to think twice before accepting that generous dinner party invitation from the welcoming Italian couple. They might get more than they bargained for. If a new report is to be believed, it seems a quarter of all Italian couples regularly take part in wife swapping.

The revelation comes not from the seedier quarters of the country that gave the world Casanova, but from the usually po-faced pages of national broadsheet La Stampa. According to yesterday's front page article, entitled "The Lunch Time Swingers", an estimated 500,000 Italian couples are officially swapping partners at private sex clubs, with thousands more doing it in a more ad-hoc fashion in car parks, specially designated beaches or even cemeteries.

The report will have Italy's Catholic clergy shaking with anger at the congregation from their pulpit but when you consider the country's lothario leader, Silvio Berlusconi, it is perhaps not entirely surprising. This is the man, after all, who – in front of the international press corps gathered in the opulent quarters of Palazzo Chigi (the Italian version of Downing Street) – once tried to pimp his wife Veronica to the Danish Prime Minister, Anders Fogh Rasmussen.

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"Rasmussen is the most handsome Prime Minister in Europe. I think I will introduce him to my wife because he is even more handsome than Cacciari," Mr Berlusconi quipped, in a reference to his wife's alleged but subsequently denied fondness for the former mayor of Venice, Massimo Cacciari.

The La Stampa article, primly struggling with whether to call this new Italian predilection a "passion" or a "hobby", said wife swapping had increased everywhere "at a rate that makes you dizzy", largely because of the internet which had stripped away the taboos.

The source with which the newspaper arrived at the one-in-four figure was a Rome-based body called The International Federation for the Protection of Rights and Freedoms, or Federsex, for short. The organisation has 500,000 members that meet in 200 private clubs across Italy and swap partners, but the Federsex experts believe that is just the tip of the iceberg. They put the real figure closer to two million, or a quarter of the eight million sexually active couples across the country.

The average age of male participants is 43, while the swapped women tend to be younger at 35, and it is no longer a furtive after-dark activity but one that can "even take place during one's lunch hour." As one employee of the Club Malizia in Milan confirmed, "We see all sorts of people ... the thing that links them is that they have no money worries – accountants, doctors, even footballers and politicians."

The La Stampa investigation was triggered by the death last month of 27-year-old Dejan Delijevic, who was found hanging by his studded dog collar from a metal fence by the Magic Nuar club on the outskirts of Mantova. Appearing to be a sex game gone wrong, it was a case that titillated the nationà la Max Mosley, prompting the same soul-searching over sexual mores.

Establishments such as the Magic Nuar, far from being an aberration, are very much part of the married life of many an Italian couple, according to La Stampa. Lara, who grew up in the Sicilian town of Catania, recounted how she felt herself suffocating during her traditional upbringing, her father requiring her to be home by 9.30pm. She fled as soon as possible to a university education in Rome during which she met Luca, the man who introduced her to wife swapping.

Nowadays, Lara and her husband Luca leave the kids at home and go out for the night to have, as she puts it, "a nice evening of group sex."

Italy's most infamous player, Signor Casanova, once said "cultivating whatever gave pleasure to my senses was always the chief business of my life; I never found any occupation more important".

In these modern days, the catchphrase might be, to quote, one scambisti: "I love my husband. That is why I want to swap him."