AS a title, In the Closet of the Vatican sounds more like a follow-up to The Thorn Birds than a game-changing piece of investigative journalism. The bestselling 1970s novel by Coleen McCullough, which introduced naive church goers to the notion that some Catholic priests might have a sex life, was an international success thanks to its titillating plot. I predict a less lucrative reaction to the forthcoming book by French journalist and sociologist Frédéric Martel. But it will make for bigger headlines. Who knows, it might even change things for a church desperately in need of an injection of honesty and transparency.

For this book Martel has conducted more than 1,500 interviews in the Vatican City in Rome, and across the world. He has spoken to priests, cardinals, bishops, monsignors, papal ambassadors, seminarians and the Swiss Guard. His conclusion, which will shock some and come as no surprise to others, is that about 80 per cent of the clergy in the Vatican state are gay. In other words, the HQ of a church that will not bless same-sex relationships, and forbids its clergy to have sex lives, is riddled with hyprocisy at its very core.

Of these 80 per cent, Martel writes, some are celibate or in denial, others are living with their partners, or resort to prostitutes. A rule of thumb is that the more vehemently a cleric condemns homosexuality, the more likely he is to be in the closet himself. Hence the behaviour of the Colombian cardinal, Alfonso Lopez Trujillo. He was in the vanguard of the church’s mission to prevent gay marriage. As the dire consequences of the Aids epidemic became clear, contrary to commonsense and compassion, he refused to encourage the use of condoms. Here was someone eager to be seen to uphold traditional values. Yet Martel claims that Trujillo, who died in 2008, used male prostitutes.

There are examples closer to home, among them the late Cardinal Keith O’Brien, who pursued a similarly denunciatory anti-gay agenda, despite his own homosexuality and predatory behaviour. In fact, it doesn’t matter where you look. Throughout the Catholic church’s parishes, globally and locally, there has been the mother of all cover-ups, not just in the buttoned-up past, but right now, here, today.

You could say the church has been built on lies: countless men forced to hide who they really are, or to seek refuge in an all-male environment where they could find illicit love behind closed doors. Those clergy who were straight must have found themselves in a bewildering labyrinth of duplicity. That such depths of deceit have been allowed to thrive says all you need to know about the controlling power of those at the heart of the church.

Martel believes that Pope Francis has earned enemies by adopting a very untypical approach. “Who am I to judge?” he replied, when asked if he condemned homosexuals, thereby loosening the ground beneath the feet of those in the Holy See who don’t want their secrets aired, or their way of life altered.

The revelation of such widespread double standards is an echo of the medieval church’s calamitous abuse of power and wealth. Out of it has sprung a culture where bullying, intimidation and blackmail have flourished. And if that has been going on in this sphere, you can be sure it will have spilled over into every other part of the church’s affairs.

In the wake of the revelation of child abuse on a grand scale in the church, you begin to see why hiding the truth was the default position. This is not to make a link between homosexuality and child abuse but to see why the ecclesiastical authorities were so quick, and adept, at making the problem disappear. In avoiding scandal, they were intent on protecting their own rather than those who had been so grievously harmed.

With evidence of institutionalised deception of the extent Martel claims, the church brings shame on itself: not for the numbers of priests who are gay, but for the willingness to lie about it, and to break vows, and the spirit of vocation, to an extent that will appall devout parishioners.

Now is the time for the Catholic Church’s own Reformation. No-one can any longer doubt that the life expected of a Catholic priest is unhealthy. And since there is no biblical injunction on him to be celibate, why can this not be changed? Already the church is embracing married Anglican vicars in flight from the ordination of women. Why not allow Catholic clergy the same right to open relationships, whether they be gay or straight?

Until the double-speak on which the modern church stands is addressed, there is no hope of winning back the faithful who have lost all trust and respect in this once revered institution. Obliging men to profess one thing while being another, is psychological torment. The denial of clergy’s humanity and self-expression is as cruel as anything the Inquisition devised. If the Vatican could bring itself to accept homosexuality, and gay marriage, and a non-celibate priesthood, it would be a truly Christian act.

Read more: Cardinal Keith O'Brien asked for forgiveness