(By Paul Virgo) Rome, August 6 - An interview with a supreme court judge on last week's decision to uphold a tax-fraud verdict against Silvio Berlusconi has stirred a huge furore, with one of the ex-premier's lawyers saying it casts doubt on the legitimacy of the decision. Sources at the supreme Court of Cassation, however, said that nothing can change the four-year jail sentence for Berlusconi - three of which have been commuted because of an amnesty - as it is now definitive. Judge Antonio Esposito spoke about the case - regarding a system of inflated film-rights purchases at Berlusconi's Mediaset media empire and the use of offshore companies to create slush and dodge taxes - in an interview with Naples-based daily Il Mattino. It is a highly unusual move as a court usually only comments on its sentences in a written explanation generally published over a month after the verdict is announced. In the interview published Tuesday, Esposito denied claims there was no evidence Berlusconi knew of the fraud and was convicted on the basis of the logic that, as the head of Mediaset, he "could not have not known" about the wrongdoing. "No, you were made aware of what was happening," Esposito, who was the head of the five-judge Cassation panel that made the tax-fraud ruling, was quoted as saying by the newspaper. However, Esposito said he was misquoted by Il Mattino, which also quoted him as saying "Berlusconi was convicted because he knew, not because he couldn't not know", although the editor said he has proof the material was correct. The interview prompted a hail of indignation from Berlusconi's supporters. "This is obviously very serious and unprecedented," said Niccolò Ghedini, one of Berlusconi's lawyers and an MP for the ex-premier's People of Freedom (PdL) party. "The competent bodies must urgently verify what happened, which cannot not have concrete effects for the evaluation of that sentence". But the Cassation sources said the interview "does not invalidate, nor change, the decision on the Mediaset trial", adding that the verdict was passed by a panel of judges, not just one member of it. Nevertheless, Justice Minister Anna Maria Cancellieri requested clarification from the supreme court over the interview, Cassation President Giorgio Santacroce told ANSA. Santacroce added that Esposito was "inopportune". Three non-magistrate members of the judiciary's self-governing body, the CSM, called on it to open disciplinary proceedings over the case. "A panel of judges should speak with legal documents i.e. the explanation of the sentence," said Bartolomeo Romano, one of the three. Rodolfo Sabelli, the head of judges union ANM, said the interview would have no effect on the tax-fraud ruling. He also said Esposito was not in danger of sanctions, while stressing that "it is opportune for magistrates handling a trial to abstain from making comments on them, especially when they are particularly high profile". Some Berlusconi supporters said something so unusual could only happen in a case involving the three-time premier, adding that this gave grounds to their assertion that he is the victim of persecution from politically motivated left-wing elements in the judiciary. Berlusconi has been at the centre of over two dozen criminal cases since he entered politics two decades ago, but last week's was the first definitive verdict against him. The PdL whips in parliament, Renato Schifani and Renato Brunetta, said in a statement that the episode showed the party's calls for justice reforms had to be satisfied.