A convicted paedophile accused of raping a five-year-old boy a month after being freed from jail said that he had been prescribed Viagra by a prison doctor.

Francis Evrard, 61, was found with a packet of the drug after being arrested for allegedly kidnapping and assaulting the boy.

Evrard, whose most recent conviction for sexual crimes was only three years ago and who had been described as one psychiatrist as “barely readaptable”, told detectives that he had been given a prescription for the pills in prison after telling a doctor there that he had erection problems.

The case of Evrard - described at his trial as an “incorrigible hunter of young boys” - has caused uproar in France.

Rachida Dati, the Justice Minister, announced an official inquiry yesterday. President Sarkozy has summoned ministers to a meeting today.

Ms Dati, who travelled to Lille in northern France yesterday to talk to those involved in the case, said: “We will find out the truth about the Viagra affair.”

The boy was snatched from the streets of Roubaix, near Lille, last weekend. He was found - with Evrard in a garage used by the man - thanks in part to a new French alert system for missing children.

Evrard’s claims about the origin of his Viagra have intensified a debate about how to treat paedophiles. Proposals to toughen sex crime laws in France include forcing repeat offenders in paedophile cases to take hormone medication while in prison.

“If it’s true, it’s totally scandalous when you consider what sort of man he is,” said Emmanuel Riglaire, the lawyer who is representing the kidnapped boy.

“The family is disgusted and worried that someone like this could have been prescribed Viagra. It’s the world upside down.”

Jérôme Pianezza, Evrard’s lawyer, said: “He explained very clearly that he asked for these products in prison, that he was given a prescription and that he got them once he was out. It’s true it’s surprising.”

However, Edouard Herszkowicz, a doctor who specialises in treating sexual offenders, said: “I can’t see a prison doctor giving him this when a chemical castration would be more appropriate. It’s much more likely that he got the Viagra once he had been released.”

The boy was found by police on the night of his disappearance after a taxi driver recognised his description from the nationwide alert. The boy was with Evrard and had allegedly been forced to take sleeping pills before being assaulted.

The suspect has been placed under formal investigation for “kidnapping, illegal detention, rape and sexual assault”.

Amid a national outcry, Mr Sarkozy has summoned ministers to a meeting today to discuss how to prevent paedophiles from reoffending.

He called the meeting a day after returning from a two-week holiday in the United States after it emerged that Evrard had been released on parole in July despite evidence that he remained attracted to children.

Evrard had served 18 years of a 27-year sentence for raping two boys. He was described as an “incorrigible hunter of young boys” by a prosecutor at his trial in 1989. He also has three other convictions for sexual crimes in 1975, 1985 and 2004. The latter offence was committed in Caen prison, where he was discovered with child pornography on his personal computer in his cell.

A psychiatrist who examined him for the court hearing in 2004 said that he had a “homosexual paedophile perversion causing a danger of a crime”. The psychiatrist added that Evrard was “barely readaptable”.

Nevertheless, he was given probation on condition that he remained in Rouen, Normandy, and had hormonal treatment in an attempt to curb his sexual desires. But within a month he had moved to Lille under a false identity. Ms Dati said that the French authorities would clamp down on paedophiles after Evrard’s arrest. “The President has been clear: the fight against sexual offenders is a priority for the Government,” she said.

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