Carmelo Abbate spent months undercover documenting a "hidden world"
in which heterosexual priests have children with women who can never be
their wives, and gay priests of many different nationalities visit
nightclubs in Rome and pay for sex with escorts.
His book, "Sex and the Vatican: a secret journey in the reign of the
chaste", was published in Italian yesterday.
Two British publishers are interested in buying the rights.
"The purpose of the book is not to shame Catholic clergy, it is to expose the hypocrisy and double standards of the Church," Mr Abbate, an award-winning investigative reporter, told The Daily Telegraph.
"There are priests with children but the kids cannot talk to their fathers in public for fear of their situation being discovered.
"There is a culture of 'omerta' (silence) in which the Church pretends
not to know about any of this. If the authorities do find out, they just
cover it up so as to avoid any scandal."
The book developed from an investigation conducted by Mr Abbate last year in which he used hidden cameras to film three priests attending gay nightspots in Rome and having casual sex, before donning their cassocks the next day and holding church services.
"At the time the Church said that these were just isolated incidents. I wanted to explore whether that was true and what I was found was that the phenomenon is much, much wider," he said.
He cited research which suggests that as many as a third of Catholic priests in the United States are gay and a quarter are in heterosexual relationships with women.
Similar statistics have been reported in Germany and Austria.
Women made pregnant by priests told him of being forced to have abortions, or having to put their children up for adoption in a desperate attempt to keep their relationships secret.
Some priests pay ex-lovers hush money so as not to be found out while others covertly support their illegitimate children through school, the book claims.
"For a lot of priests, the Church's teachings on sexual relations are a prison," said Mr Abbate.
The Vatican declined to make any comment on the book, while a spokesman for the Italian Bishops Conference said: "We can't react to all books that speak badly of the Church."
The book developed from an investigation conducted by Mr Abbate last year in which he used hidden cameras to film three priests attending gay nightspots in Rome and having casual sex, before donning their cassocks the next day and holding church services.
"At the time the Church said that these were just isolated incidents. I wanted to explore whether that was true and what I was found was that the phenomenon is much, much wider," he said.
He cited research which suggests that as many as a third of Catholic priests in the United States are gay and a quarter are in heterosexual relationships with women.
Similar statistics have been reported in Germany and Austria.
Women made pregnant by priests told him of being forced to have abortions, or having to put their children up for adoption in a desperate attempt to keep their relationships secret.
Some priests pay ex-lovers hush money so as not to be found out while others covertly support their illegitimate children through school, the book claims.
"For a lot of priests, the Church's teachings on sexual relations are a prison," said Mr Abbate.
The Vatican declined to make any comment on the book, while a spokesman for the Italian Bishops Conference said: "We can't react to all books that speak badly of the Church."