Italy's highest appeal court has denied a woman alimony – because she once discussed the idea of an open marriage with her husband before they married.

The court heard that the woman had "theorised" that marriage did not have to be based on sexual fidelity, but had never put the idea into practice.

"We fully support the lower court's findings, even though there was no evidence of the woman frequenting other men," the Cassation court said in a precedent-setting ruling today.

The couple's Catholic wedding was annulled by an ecclesiastical court in Modena due to the woman's ideas on faithfulness, even though the man had willingly tied the knot.

Fearing the loss of alimony, the woman appealed against the annulment in Italy's civil courts, only for them to back the church's ruling.

"I find it shocking and very perplexing that the court should rule on what is a virtual betrayal when real betrayals frequently go unpunished," Gian Ettore Gassani, the chairman of the Italian association of matrimonial lawyers, said.

Catholics who divorce in civil court are not allowed to remarry in church, prompting many to ask ecclesiastical courts to annul their marriages on the grounds that they were never truly valid.

Annulments in Italy hit a peak of 8,000 in 2008, up from around 2,000 a decade ago, Gassani said, thanks to some spurious claims including husbands being too attached to their mothers, use of cannabis by one spouse and unwillingness to have sex.

"It had descended into anarchy as people realised that it could be quicker and cheaper to get an annulment through the church than a divorce through Italy's sluggish courts," he added.

Gassani said "repeated" appeals by Pope Benedict XVI to his ecclesiastical courts to stop handing out easy annulments meant only 6,000 were granted last year – part of a worldwide total of around 40,000.

"But virtual betrayal still made it through and was then upheld in a civil court, showing that we appear to be in the hands of judges with some very strange views," he added.