By David Willey BBC Rome correspondent

More than 100,000 left-wingers have held a protest meeting in Rome against Prime Minister Berlusconi's decision to push a law through parliament to delay his trial on corruption charges.

The rally for Legality and Justice was organised not by politicians, but by one of Italy's best-known film directors, Nanni Moretti.

Moretti has become the unofficial leader of the anti-Berlusconi movement

The police said 100,000 people filled the piazza and the organisers claimed four times that number.

But, by any account, this was a powerful demonstration of public opposition to Mr Berlusconi's right-wing coalition.

There were more singers, actors, artists, journalists and musicians on the platform than politicians - a sign that part of the anger of Italy's middle classes against Mr Berlusconi is directed as much against the political parties of the left for failing to carry out an effective political opposition, as against Mr Berlusconi himself.

Inevitably, the demonstration also took on the tones of an anti-war protest.

Mr Berlusconi is in the United States seeing President George W Bush to agree on Italy's support for the war against international terrorism.

Italian public opinion is heavily against joining in any military action against Iraq.

Pressure for new party

The atmosphere was festive and relaxed with the emphasis on entertainment as well as politics.

The problem of the Italian left is that traditionally it has been dominated by the trade unions.

Critics say Berlusconi's reforms are motivated by self-interest

With the change-over from a predominantly blue-collar to a white-collar economy over the past two decades, the new left-wing parties - successors to the former Communists and Socialists - have failed to inspire confidence among the new middle and working class who live off service industries, not manufacturing.

Some political commentators are saying that Saturday's protest could signal that the time is right for the creation of a new left-wing party to balance Forza Italia, the right-wing party set up from scratch by Silvio Berlusconi 10 years ago, which is now in power.