Disgraced ex-premier Silvio Berlusconi made a 20-year pact with Mafia bosses to whom he paid millions of euros in exchange for protection and help with his business empire, according to a judicial report.

The tycoon’s deal with the mob was described by judges of the Palermo Appeals Court as part of their 476-page reasoning, released on Thursday, behind the jail sentence for his Mafia association given to Berlusconi’s close friend Marcello Dell’Utri.

The judges say that Dell’Utri, a Palermo-born former senator in Berlusconi’s PDL (People of Freedom) Party, was the mogul’s go-between with the Cosa Nostra for 20 years, up until 1992, the year in which the Mafia assassinated two prosecutors in bomb attacks.

Download the new Independent Premium app Sharing the full story, not just the headlines

The report follows a dreadful summer for the three-time prime minister. In June he was found guilty of paying for sex with an under-age girl and abuse of office in the “Rubygate” affair. In August, he was definitively convicted of tax fraud, for which he is due to serve a year of house arrest or community service, and is also likely to be expelled from parliament.

Political pundit James Walston, of the American University of Rome, described the report as “another nail in the coffin of Silvio Berlusconi”.

Dell’Utri, 73, was sentenced to seven years in prison for Mafia collusion in March this year by the Palermo Appeals Court. He denies the charges and will appeal the verdict at the Supreme Court.

The Palermo judges Dino Lo Forti, Daniela Troja and Mario Conte say in their detailed reasoning, however, that the former senator’s pivotal role as Berlusconi’s envoy to the Cosa Nostra, which saw him help “pour millions of euros of Berlusconi’s money into the Mafia’s coffers” was “beyond reasonable doubt”.

The pivotal episode was the encounter in Milan in 1974 between up-and-coming businessman Berlusconi and the senior Cosa Nostra figures Gaetano Cinà and Stefano Bontate, which Dell’Utri organised.

It was at this meeting that a deal was struck giving Mr Berlusconi protection from criminal threats, as well as help with his construction business and broadcasting plans in Sicily, in return for large amounts of cash.

The judges also note that Dell’Utri introduced the known mafioso Vittorio Mangano to Berlusconi and got him a job as the stableman at Berlusconi’s villa in Arcore, outside Milan. Mangano’s real job, they say, was as the Cosa Nostra’s “representative” in Arcore, probably with the additional role of deterring kidnappers.

Leading Mafia writer Attilo Bolzoni said in La Repubblica newspaper: “What we knew for a long time regarding the protagonists in this story, Cosa Nostra bosses on one side and a Milan businessman and three-time prime minister on the other, has now acquired an official stamp.”

The report says Dell’Utri, who helped Berlusconi found his Forza Italia! Party, the forerunner to the PDL, has “a natural predisposition to actively enter into contact with mafiosi”.

Berlusconi is unlikely to be tried for Mafia association because the statute of limitations does not allow prosecution for alleged crimes that occurred more than 20 years ago, unless they carry a life sentence.

But his legal difficulties are far from over. He is currently being investigated over claims he bribed the former senator Sergio De Gregorio to change political parties and help bring down Romano Prodi’s 2006-2008 centre-left government.