Well may the pope defy “the petty gossip of dominant opinion.” But the Holy See can no longer ignore international law, which now counts the widespread or systematic sexual abuse of children as a crime against humanity. The anomalous claim of the Vatican to be a state—and of the pope to be a head of state, and hence immune from legal action—cannot stand up to scrutiny.

The truly shocking finding of Judge Murphy’s Commission in Ireland, tasked with investigating child sex abuse in Dublin’s archdiocese, was not merely that “sexual abuse was endemic in boys’ institutions,” but that the church hierarchy protected the perpetrators and, despite knowledge of their propensity to reoffend, allowed them to take up new positions teaching other vulnerable children after their victims had been solemnly sworn to secrecy. This, of course, amounted to the criminal offence of aiding and abetting sex with minors.

Head of state immunity provides no protection in the International Criminal Court.

In legal actions against Catholic archdioceses in the U.S., it has been alleged that this reflected Vatican policy as approved by Cardinal Ratzinger (as the pope then was) as late as November 2002—sexual assaults were regarded as sins that were subject to church tribunals and guilty priests were sent on a “pious pilgrimage” whilst oaths of confidentiality (“papal secrecy”) were extracted from their victims.

In the U.S., 11,750 allegations of child sex abuse have so far featured in actions settled by archdioceses (in Los Angeles for $660 million and in Boston for $100 million), but some dioceses have gone into bankruptcy and some claimants want Vatican accountability—two reasons to sue the pope in person. But in 2005, a test case in Texas failed because the Vatican sought and obtained the intercession of President George W. Bush, who agreed to claim sovereign (i.e., head of state) immunity on the pope’s behalf. Bush lawyer John B. Bellinger III certified that Pope Benedict XVI was immune from suit “as the head of a foreign state.”

The third Mr. Bellinger is notorious for his defense of Guantanamo and Bush administration torture policies, and his opinion on papal immunity is even more questionable. It hinges on the assumption that the Vatican or its metaphysical emanation, the Holy See, is a state. But the Papal States were extinguished by invasion in 1870 and the Vatican was created by fascist Italy in 1929 when Benito Mussolini endowed this tiny enclave—0.17 of a square mile containing 900 Catholic bureaucrats—with “sovereignty in the international field... in conformity with its traditions and the exigencies of its mission in the world.”

The notion that statehood can be created by another country’s unilateral declaration is risible. If it weren’t, Iran could make Qom a state overnight and the U.K. could launch the city of Canterbury on to the international stage by the same process. But it did not take long for Catholic countries to support the pretentions of the Holy See, sending ambassadors and receiving Papal Nuncios in return. Even the U.K. maintains an apostolic mission that, until 2005, was always filled by British Catholics.

The U.N. at its inception refused membership to the Vatican (U.S. Secretary of State Cordell Hull said emphatically that it could never attain statehood) but has allowed it a unique and anomalous “permanent observer status,” permitting it to become signatory to treaties like the Law of the Sea and (ironically) the Convention on the Rights of the Child, and to speak and vote at U.N. conferences, where it promotes its controversial dogmas on abortion, condoms, and homosexuality. This has involved the U.N. in blatant discrimination on grounds of religion, as other faiths are unofficially represented, if at all, by NGOs. But it has encouraged the Vatican to claim statehood—and the immunities from liability that attach to heads of state.

This claim could be challenged successfully in the U.K. if the pope is served with a writ when he visits there in September. Unlike overly deferential American judges, British courts do not accept the executive’s word on who gets immunity. Had Chile's General Pinochet gone to New York instead of London, the White House would have stopped his extradition proceedings immediately rather than allowed him to be detained for 18 months while the courts determined that as a former head of state he could not claim immunity from torture charges.

In any event, head of state immunity provides no protection in the International Criminal Court (hence its current indictment of President Bashir). The ICC statute defines a crime against humanity to include rape and sexual slavery and other similarly inhumane acts causing serious harm to mental or physical health committed against civilians on a widespread or systematic scale if condoned or tolerated by a government or a de facto authority. The U.N. Appeal Court in Sierra Leone has held that recruitment of children as soldiers or sex slaves for an army amounts to a crime against humanity.

If acts of sexual abuse by priests are not isolated or sporadic events but part of a wide practice both known to and unpunished by their de facto authority—i.e. the Catholic Church—then under the command responsibility principle of international law (laid down by the U.S. Supreme Court) the commander can be held criminally liable. He falls within the temporal jurisdiction of the ICC so long as that abusive practice and the policy to tolerate it continued after July 2002, when the court was established.

Pope Benedict has recently been credited with reforming the “papal secrecy” system he allegedly approved in 2002, so that guilty priests may now be reported to civil authorities, although initially (and disgracefully) he blamed the scandal on “gay culture.” His admonition last week to the Irish church repeatedly emphasised that heaven still awaits the penitent pedophile priest. The Holy See may offer the prospect of redemption to its gravest sinners, but it must be clear in law that the pope does so at his own risk—as a spiritual adviser, and not as an immune sovereign.

Geoffrey Robertson QC is author of “ Crimes Against Humanity,” published by the New Press.