Padre Pio, the friar with fingerless gloves whose image is found on a million Catholic key chains; who was canonised before 200,000 ecstatic pilgrims five years ago, was a charlatan who deliberately mutilated himself with acid to give the appearance of bearing the stigmata of Christ, according to evidence to be published next week.

The Italian historian Sergio Luzzatto will release Padre Pio, Miracles and politics in 20th century Italy – a book producing new evidence from Vatican archives, which he says proves that the charismatic friar secretly procured carbolic acid with which to burn his hands, feet and sides.

The allegations are not new: two successive popes regarded Padre Pio as a fraud. By 1920, when Pio was 33 and was already exhibiting his scars before masses of pilgrims, the church was worried that his cult was spinning out of control. Reports commissioned by the church claimed Pio regularly scourged himself with a metal-tipped whip, and had sex with women twice a week. For many years Pio was banned from celebrating mass in public.

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Of particular concern to the church were the ugly, weeping wounds which Pio concealed under those fingerless gloves. The friar claimed that he had received the stigmata of Christ – wounds to his hands, feet and side like those suffered by Christ during his crucifixion – at the culmination of a mystical seizure.

A doctor sent by the Vatican to examine them concluded that the wounds were probably caused and maintained artificially. To test the hypothesis he bound the wounds and sealed the bandage to prevent it being tampered with. But on examination a month later the doctor was nonplussed to find that the wounds had failed to heal.

Yet now Mr Luzzatto claims to have unearthed documents that prove beyond reasonable doubt that the friar was a trickster.

In the summer of 1919, the 28-year-old cousin of a pharmacist in the southern city of Foggia, a deeply religious young woman called Maria de Vito, made the pilgrimage to Pio's church, San Giovanni. The pharmacist told his local bishop, Mgr Salvatore Bella, "When she returned to Foggia she brought the greetings of Padre Pio and asked me in his name, and in strict secrecy, for carbolic acid, telling me that Padre Pio had need of it, and giving me the little bottle he had given her, capacity 100g, and with a skull and crossbones."

The pharmacist jumped to what Mr Luzzatto believes is the right conclusion. "My thought was that the carbolic acid could be used by Padre Pio to procure or further irritate wounds on his hands."

Mr Luzzatto cites the note written by Pio to the young woman, Maria de Vito, "though much more neatly than his normal hand".

Invoking the blessings of Jesus, Pio writes baldly: "I am in need of 200g or 300g of carbolic acid for sterilising. I pray you to send it to me on Sunday." This, claims Mr Luzzatto, is the smoking gun. If he had really needed the acid for sterilising purposes, he demands, "why did he proceed in such an oblique manner?"

Mr Luzzatto's claims, splashed across a full page of Corriere della Sera, Italy's best-selling daily, were furiously denounced by Pietro Siffi, president of the Catholic Anti-defamation League. The "presumed proofs are absolutely false," he said. "According to Catholic doctrine, canonisation involves the infallibility of the pope."