By David Willey BBC, Rome

An Italian senator is touring the country trying to gather a million signatures for a national referendum on whether to cancel a new law giving Prime Minister Silvio Berlusconi immunity from prosecution.

Di Pietro needs 500,000 signatures by the end of September

Antonio di Pietro was famous a decade ago as the public prosecutor who carried out a crusade against political corruption in Italy.

He caused a minor political revolution when the two political parties which had governed Italy almost uninterruptedly since the fall of fascism - the Christian Democrats and the Socialists - were forced to dissolve themselves as a result of his prosecutions.

Both local and national politicians were implicated in what came to be known as the bribesville scandal, or Tangentopoli in Italian.

Megaphone

Mr Di Pietro is now mounting a political mini-crusade against billionaire businessman Mr Berlusconi.

He is currently on a whistlestop tour of Italy armed only with a megaphone and some paper for collecting signatures.

He told me he has some 5,000 supporters who have given up their summer holidays to work for his reformist political party.

The party takes its inspiration from a phrase of the former American president, John F Kennedy, "Ask not what your country can do for you, but what you can do for it".