Former chief executive Donald Tsang Yam-kuen allegedly tried to secure a private audience with the pope in 2008 with the help of a close political associate of disgraced Italian ex-prime minister Silvio Berlusconi.
But in return, Tsang's administration was asked to help stop the transfer of evidence seized in Hong Kong to Italian public prosecutors investigating a fraud and money laundering case linked to Berlusconi.
The claims are made by former Italian senator Sergio De Gregorio, who is himself embroiled in a corruption probe after he admitted accepting €3 million (HK$31 million) in bribes from the shamed ex-premier.
Tsang denied knowledge of De Gregorio's claims, and Hong Kong officials said the government would never get involved in a criminal investigation.
De Gregorio said that between 2007 and 2008 he met high-ranking Hong Kong officials in Rome including Duncan Pescod, who was the city's representative to the European Union, and his successor Mary Chow Shuk-ching.
The allegations centre on a lunch at De Gregorio's Rome residence in April 2008 at which Pescod requested the senator's help in securing an audience for Tsang with Pope Benedict XVI.
The senator, in return, asked the Hong Kong government for its help regarding the Berlusconi investigation. Shortly afterwards, De Gregorio said he received a letter from Pescod, thanking him for the lunch. "The letter suggests Pescod had acted on matters relating to the interests of Berlusconi," De Gregorio alleged.
The claims are contained in two transcripts of interviews with the former senator obtained by the South China Morning Post.
The questioning was conducted by prosecutors in Naples over claims of vote-buying in 2008. De Gregorio bragged about knowing senior officials in the Hong Kong government.
He also told Berlusconi he could send "messages to these gentlemen to make them understand that the head of the Italian opposition does not deserve such treatment by Hong Kong authorities", according to the transcript.
Tsang denied the allegations yesterday, saying he "has never written through Mr Pescod to Pope Benedict and requested an audience". Tsang said he did not know De Gregorio.
But Pescod, now permanent secretary for transport and housing, confirmed he helped Tsang to seek a meeting with the pope at a lunch with an Italian senator from Berlusconi's party in 2008, although he could not recall the senator's name.
"The Brussels Economic and Trade Office was involved in an attempt to arrange an audience for the former CE [Tsang] with the former Pope [Benedict XVI] ahead of a possible visit to Rome, but this was not successful," Pescod said in a reply to a South China Morning Post inquiry.
"During the process, together with colleagues from the Brussels Economic and Trade Office, I made a visit to Rome and met a number of senior people … The senator offered to help but made a link to a case then being investigated in Hong Kong involving Berlusconi."
Pescod said he made it "very clear that the government would not intervene in any ongoing criminal investigation" and denied there was any link between the request for the audience and any criminal investigation involving Berlusconi.
"The senator was told that the judiciary in Hong Kong operated without any interference from the government given the separation of executive and judicial functions," he said.
Chow confirmed she met De Gregorio twice in October 2008 in Rome in an official capacity, but denied discussing any legal proceedings involving Berlusconi.
There was no evidence the Hong Kong government ever tried to influence the legal proceedings involving Berlusconi.
But the Italy side did make efforts to set up a meeting between Tsang and the pope, according to De Gregorio.
He said Monsignor Eugene Nugent, head of the Holy See's study mission in Hong Kong, was against the meeting. But a meeting was scheduled after De Gregorio approached Monsignor Pietro Parolin, who was then the Vatican's Undersecretary of State for Relations with States. However, Tsang cancelled the audience at the last minute on the orders of Beijing, he said.
De Gregorio's claims could be supported by what a Catholic Church official told the Post in 2010. The church official said the Holy See scheduled a private audience with Tsang in 2008, but the meeting was cancelled later for unknown reasons.
The Vatican and Beijing had a row about the same time over the Chinese Catholic Patriotic Association's celebration of the 50th anniversary of China's first unilateral ordination of bishops without the pope's approval.
Two years later, in 2010, Tsang again cancelled a scheduled meeting with the pope because he had to stay in Hong Kong to solve a political crisis.
Tsang, a devout Catholic, had always wanted to meet the Pope for a dialogue and blessing. But he could do so only in a personal capacity as the Vatican has no diplomatic ties with Beijing.
This raises the question of in what capacity Tsang requested Pescod and other Hong Kong officials to act on his behalf to seek the audience. Some mainland experts also questioned this and said it was a departure from normal diplomatic protocol.
Professor Su Hao, of China Foreign Affairs University, said the military and foreign affairs of Hong Kong must be handled by the central government in Beijing as stipulated in the Basic Law.
He said the consensus and approval of the Foreign Ministry in Beijing, or the Officer of the Commissioner of the Ministry of Foreign Affairs in Hong Kong, should be obtained if a senior official wants to meet heads of states who have no diplomatic ties with China.
Additional reporting by Tony Cheung, Teddy Ng