It was a big day yesterday in British politics, with David Cameron’s speech to the final day of the Conservative Party annual conference. But The Times of London chose to lead its front page not with local news, but with the story of Silvio Berlusconi’s judicial setback, in which Italy’s constitutional court invalidated a law on prime ministerial immunity.

Berlusconi’s government had passed the law to protect him from judicial attack while in office: he was already facing two prosecutions, one an apparently credible case of bribery, and there are further allegations of fraud, corruption and tax evasion. But the court found that it violated the constitutional requirement for equality before the law.

Although Berlusconi has never been convicted, his relationship with the courts in his three terms of office has been tempestuous, and the immunity law was not the first time he had resorted to legislation in an apparent attempt to frustrate charges against him. Not surprisingly, he attacked Wednesday’s decision as politically biased, promising to “make my accusers look ridiculous and show everyone what stuff they are made of and what stuff I am made of.”

His legal problems have not kept Berlusconi from political success: he was the only Italian prime minister in fifty years to hold office for a full term of parliament (2001-06), and last year he was returned to power with a substantial majority. But outside Italy he seems to have few friends. The Times’s foreign commentator, Bronwen Maddox, was particularly scathing, saying his actions “had begun to support a serious case that Italy offended the EU’s founding principles of democratic government.”

But the idea of judicial immunity for a country’s leaders is by no means unprecedented. It was one of the principles at stake in America in the Paula Jones case of the 1990s, when Bill Clinton’s lawyers argued, ultimately without success, that civil litigation against a sitting president should not be permitted due to the distraction it could cause from their job. Later developments showed that the argument was not without merit.

In criminal cases, the position of a US president is less clear: there is the possibility of impeachment, and the courts have not had to rule on whether criminal prosecution would also be possible. (In the case of Richard Nixon, the prosecutors chose not to make the attempt, and he was named by the grand jury as an “unindicted co-conspirator”.) But several other heads of state, including notably the French president, enjoy immunity while in office.

The difference for Berlusconi is that he is not head of state — just head of government, in the same position as an Australian prime minister. Moreover, the fact that Italy has a Westminster system of government removes the practical possibility of impeachment, since Berlusconi would not be in office in the first place unless he had a parliamentary majority.

That makes the case for immunity much less persuasive. Italians may have voted for him, but if their prime minister is a crook, the courts need to be given the opportunity to say so.