The Italian Left has accused Silvio Berlusconi, the Italian Prime Minister and media tycoon, of "moving towards dictatorship" by pushing through Parliament a law granting himself immunity from prosecution.

The Senate gave final approval on Tuesday night to a bill halting criminal trials against the holders of the four top offices of state — the President, the Prime Minister, and the Speakers of the Senate and Lower House — for as long as they hold a term of office. Of the four, only Mr Berlusconi is currently being prosecuted.

The new law exempts Mr Berlusconi from a trial in Milan in which he is charged with having allegedly given David Mills, his former tax lawyer and the estranged husband of Tessa Jowell, the Olympics Minister, a $600,000 bribe to give misleading testimony in a corruption trial in the 1990s involving alleged tax fraud by Mr Berlusconi's Mediaset empire. Both men are on trial, and both deny the charge.

Antonio Di Pietro, the former anti-corruption magistrate who now leads Italy of Values, a centre Left opposition party, told The Times that Mr Berlusconi, 71, who won elections in April to lead Italy for the third time as Prime Minister, was using his power to pass laws to his own benefit, as he had when previously in office.

"Taken with other planned measures, the law giving him immunity is a move towards dictatorship," he said. "Berlusconi is placing himself above the law. Italians have the right to know if their Prime Minister is or is not a criminal".

Mr Di Pietro contested the government's assertion that the immunity law merely brings Italy into line with the rest of Europe. "Name one other European country where the Prime Minister is above the law," he said. Anna Finocchiaro, head of the opposition Democratic Party in the Senate, said that the law made Mr Berlusconi "a sovereign monarch without limits".

Walter Veltroni, the opposition leader, said that at a time when Italy faced critical economic problems Mr Berlusconi was "using his power to protect his own interests instead of addressing those of the country".

However, aides to Mr Berlusconi said that the measure would allow Mr Berlusconi, who claims he is "persecuted" by biased leftwing magistrates and judges, to govern "without legal distractions". Mr Berlusconi has said that he has been subjected to 2,500 judicial hearings and 587 visits by the police, and has paid out €174 million in legal fees.

"I'm the universal record-holder for the number of trials in the entire history of man — and also of other creatures who live on other planets," he said this month. He has won all cases brought against him so far for corruption, tax fraud and illegal party funding, either through acquittal on appeal or because time ran out under Italy's statute of limitations.

Niccolo Ghedini, Mr Berlusconi's defence lawyer, who is also a parliamentary deputy, told The Times that the judge in the case would now decide whether to proceed against Mr Mills alone. However the Berlusconi government is also tabling a bill under which "non priority" trials would be suspended for a year, a provision which could in theory be applied to the Milan bribery trial.

The new immunity bill enters into force once President Napolitano signs it. A previous law giving the top holders of state office immunity was passed in 2003 during Mr Berlusconi's last term of office but overturned the following year by the Constitutional Court.

The government claims that the new law, devised by Angelino Alfano, the Justice Minister, will this time meet the Constitutional Court's objections since it limits immunity to a single term in office and allows "injured parties" to seek civil damages even if a criminal case is suspended.

Critics of Mr Berlusconi say that he hopes to be elected President after Mr Napolitano when the current legislature ends, and thus secure "infinite" immunity since the head of state serves for seven years.

Mr Alfano defended the bill, saying: "To critics who have called into question the speed with which this law has been presented, I say that this law is not premature, nor too late, it is right". He said that further judicial reforms were planned for the autumn to streamline Italy's notoriously slow and inefficient justice system.

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