Pope Benedict was today accused of being involved in the mishandling of the case of a child-abusing priest in his former archdiocese of Munich, an allegation which directly links him to the burgeoning scandal in the Catholic church.

The accusation, which has been only partly denied by church representatives, cast a deep shadow over the pontiff's approaching visit to Britain. It also elicited heated protests from Roman Catholic leaders and Italian politicians.

Italy's foreign minister, Franco Frattini, said on his Facebook site that the pope was being subjected to "scandalous and disgraceful" attacks. One churchman, Antonio Riboldi, the emeritus bishop of Acerra, declared that it marked the start of a war "between the church and the world; between Satan and God".

Today's allegation arose from the case of Father Peter Hullerman, a paedophile who in 1980 was transferred to the then Cardinal Joseph Ratzinger's diocese for therapy. Instead, after just a few days, he was assigned to pastoral work.

Hullerman went on to abuse at least one boy – a crime of which he was later convicted in a secular court. When the affair came to light this month, the diocese's former vicar-general, Father Gerhard Gruber, accepted full responsibility for the mistake.

However, according to a report in today's New York Times, Benedict's office was copied in on the memo Gruber issued transferring Hullerman to parish duties. It also said that the future pope had chaired the diocesan council meeting at which it was agreed the priest should be allowed to come to Munich.

A spokesman for the archdiocese said: "The report does not contain false information, but the interpretation — that Cardinal Ratzinger knew — is pure speculation."

He added: "I do not know if any copy [of the memo] exists. But it is a usual procedure that a decision about priests goes to the office of the archbishop. But it is not usual that he takes note of every written piece of paper, every decision of the vicar-general."

A statement from the Vatican went further, saying "the then archbishop had no knowledge of the decision."

On Thursday, the pope's spokesman defended him from claims that, while still a senior Vatican official, he had opted not to try under church law a dying American priest, Father Lawrence Murphy, who abused up to 200 deaf boys. Murphy preyed on the children at a school in Wisconsin between 1950 and 1974, but the case did not reach Rome until 20 years after he was moved to other duties.

Documents posted to the New York Times's website showed that the pope's then deputy, Tarcisio Bertone, who has since become his right-hand man as secretary of state, decided to scrap the trial. This was despite opposition from Murphy's archbishop, who told a meeting in Rome that the priest remained unrepentant.

The scandal has brought out a sharp difference between the views of Italy and the Vatican on the one hand, and those of other countries. The latest allegations have emerged in Germany, where this week a poll for Stern magazine indicated that confidence in pope Benedict among Catholics had collapsed since the end of January, from 62% to 39%.

"I think he's bound to be damaged," said the British Catholic author and biographer Michael Walsh. "[The scandal] is getting closer to him." He predicted the controversy would affect Benedict's official visit to Britain in September.

"He's not popular here anyway, and I don't think he'll get a warm welcome," he said.

But in Rome, Sandro Magister, who runs a Vatican-watching web site, www.chiesa, argued that the criticism of the pope was "reinforcing his authority, both in respect of the bishops and the Catholic faithful. He is coming out of this stronger than before as a very strong, very decisive man who is seen within the church as the one who has done more than any other to fight the plague of child abuse."

Benedict's supporters point to his record since becoming pope in 2005, which they say includes a no-tolerance policy towards clerical paedophiles. Today brought a reminder in the form of a statement from the Legionnaires of Christ whose founder Benedict stripped of his priestly duties before ordering an investigation into the order that could yet lead to its suppression. The legionnaires' leadership said in a web statement: "We express our pain and regret to each and every one of the persons who were harmed by the actions of our founder."

The New York Times report — the second in two days — stirred heated rejoinders from a number of the pope's admirers, including several politicians campaigning ahead of voting in 13 Italian regions on Sunday and Monday.

Maurizio Ronconi, a leading Italian Christian Democrat, said: "For years, a masonic-secularist offensive against Catholics has been under way."

A centre-left opposition MP, Pierluigi Castagnetti, said: "It is now quite clear that the campaign against the pope and the secretary of state of the holy see by certain great foreign newspapers is not fortuitous, nor does it stem from any journalistic right or duty, but is rather a precise design intended to strike the Catholic church at the top."

Lock and key

Church records

When he was archbishop of Munich and Freising, Joseph Ratzinger would have kept secret archives on Father Peter Hullermann to comply with the code of canon law. Nestled in book two, part two, section two, title three, chapter two, article two, under the heading "The chancellor, other notaries, and the archives", are rules explaining what is to be archived, how, and who has access to it.

According to the Vatican website, each diocese should have an archive or "at least in the common archive a safe or cabinet, completely closed and locked, which cannot be removed; in it documents to be kept secret are to be protected most securely".

These contain "documents from historic criminal cases concerning matters of a moral nature; documentary proof of canonical warnings or corrections when someone is about to commit an offence, is suspected of having committed one, or is guilty of scandalous behaviour; documents relating to preliminary investigations for a penal process that was closed without trial; documents relating to any other matters the bishop considers secret". Only the bishop has a key to the secret archive.

Canon 489.2 states: that "Each year documents of criminal cases in matters of morals, in which the accused parties have died or 10 years have elapsed from the sentence, are to be destroyed. A summary of what occurred along with the text of the definitive sentence is to be retained."

It is not known whether secret diocesan archives have ever formed part of a civil claim or criminal investigation against a paedophile priest. But their existence, and the code of conduct surrounding them, sheds light on how much value the church places on record-keeping and due diligence.

John Allen, senior correspondent at the National Catholic Reporter, has suggested the Vatican heed Cardinal Sean Brady's advice and stop the "drip, drip, drip of revelations of failure" by throwing open its records and allowing investigators or responsible journalists to examine them to publicly prove, if nothing else, that the church is committed to transparency.

"The Munich archdiocese could publish a comprehensive list of every priest, diocesan and religious, who served between May 1977 and February 1982, along with whatever information church officials had at the time about any accusations against them, and what was done."

True friends of the pope, he notes, should be pressing for full disclosure.

Riazat Butt

• This article was amended on 29 March 2010. In the original we misnamed Freising as Freisberg. This has been corrected.