The story goes like this: there was once a man of humble origins, raised in an obscure corner of eastern Europe, who had an overweening ambition to become a person of world importance. Gifted with many useful talents, such as a fine ability to act (both on and off stage) and a keen nose for networking, his sense of his own importance and his desire to succeed at all costs propelled him (eventually) into a position of enormous power which he clung on to tenaciously for many years.

When he was not actively abusing his authority by secret machinations, he was passively quiescent about the abuses perpetrated by others in the name of the corporation he controlled. Now that he is dead it is the job – nay, the bounden duty – of this author to tear away the pious myths and legends that have accrued around the memory of this false prophet and expose him for what he really was.

In case the reader has not already guessed, the subject of this story is the late John Paul II.

Yallop, described in the blurb as an “investigative writer”, has made his reputation by exposing explosive facts that would otherwise be hidden – such as the murder of John Paul I in 1978, three months into his pontificate, and its cover-up orchestrated by Cardinal Villot. Despite there not being a shred of evidence for this allegation (even John Cornwell, himself no slouch at dubious investigative journalism, exposed it as false in his own book) it is declaimed on page 1 of this volume and sets the melodramatic tone for the rest of the book.

Subtitled “Inside the dark heart of John Paul II’s Vatican”, Yallop cannot quite decide who is the greater villain: the late Pope himself or his corrupt court — the “Vatican Village”. This latter is depicted as a quasi-Mafia headquarters while at the same time being “awash” with freemasons, members of the “sect” of Opus Dei, fascists and homosexuals. Reading these 500 pages is heavy-going; I could not discover one redeeming feature of this papacy, nothing to suggest that John Paul II was a great ambassador for Christ or that the Church might just occasionally do some good in the world. Even Graham Greene’s novel of the same title allows the whisky priest his moment of heroism. Here everyone who does not fit in with the author’s own brand of liberal intolerance is discredited.

The two longest chapters, predictably, concern the Vatican’s dealings with the Banco Ambrosiano and revelations of paedophilia in the priesthood. Both indisputably grave scandals, they require a more thoroughgoing, less prejudiced treatment than they receive here. Major players who pop up everywhere are Roberto Calvi, found hanged under Blackfriars Bridge in 1982 and Archbishop Marcinkus, who ran the Vatican Bank. If these two characters had not existed, the author would have had to invent them. When he is not preoccupied with sex and violence he loses his focus but never his venom. He manages to taint everything he touches. Thus World Youth Days are compared to Nazi Nuremberg rallies; the Pope’s love for the Blessed Virgin is “infatuation” or worse, “idolatry”; Providence is a “good contact, a patron or a protector”.

The usual dreary syllabus of Catholic errors and malefactions is trotted out, such as the ban on birth control, women priests and the right to abortion; the elderly celibate men who run the Church; the “neutering” of Hans Kung by the “Vatican Enforcer”. Polly Toynbee, post-Enlightenment high-priestess, is quoted approvingly: “How many people have died of AIDS as a result of Wojtyla’s power?”

Vatican sources, always anonymous, tell the author that the Pope won’t retire, despite his infirmity, because he is “terminally drugged on the adulation of the audience”. Even the captions to the book’s photographs carry a gratuitously unpleasant slant, such as “The Holy Alliance that never was” underneath a picture of John Paul II with President Reagan. In case you did not know, the part these two played in the collapse of Communism is “a myth”. In case you thought the Pope acted as a peacemaker in the world – condemning the Iraq war, for instance — that also is a myth.

Despite numerous accusations, quotations and allegations, Yallop’s documentation is scanty; there are only 13 notes throughout the whole book. Apparently he has consulted many papal encyclicals and other documents, yet for all his understanding they might just as well have been hieroglyphics. What he lacks in interpretative skill is compensated by fevered phrases: the Pope was “given to bitterness”, he was “quivering with anger”, Ratzinger was “reduced to tears”, the Church had a “lust for temporal power”. The book is also rambling and repetitive; in his zeal to blacken every aspect of the Holy Father’s life, Yallop cannot resist gloatingly repeating his punch-lines. The editing is sloppy: Bishop Deskur had a “major stoke”, the Legionaries of Christ become “Legionnaires” and there is reference to a “Head of Viligance”. If this were Shakespeare’s Dogberry one would laugh.

But this is not comedy. Although described on the dust-jacket as “History/Biography” it is neither; it is simply sensational journalism at its very worst. There are undoubted criticisms to make of the late papacy; there is also the possibility of an intelligent outsider producing a balanced appraisal – as Anthony Howard does, for instance, in his biography of Basil Hume. But this is not the book and Yallop is not the man. A denizen of Grub Street, he has grubbed around in the shadows, giving his own lurid and sordid spin to men and events.

How did I feel when I had finished reading it? Distinctly grubby.

Francis Phillips writes from Bucks in the UK.