Mr Colombo, a former president of the European parliament said he used the drug for "therapeutic purposes".

His disclosure was made voluntarily to prosecutors investigating a ring alleged to have supplied drugs and prostitutes to high society figures.

The investigation has already seen allegations levelled at a junior minister in Silvio Berlusconi's rightwing government, a former porn star and the owner of one of Rome's most fashionable restaurants.

Sources close to the inquiry said other famous names remain - for the moment - locked away in the prosecutors' files.

But Mr Colombo is in a class of his own. Earlier this year, he received Italy's highest political honour when the president, Carlo Azeglio Ciampi, gave him a permanent seat in the upper house of parliament as a senator for life.

Mr Colombo led Italy between 1970 and 72 and has held almost every senior ministerial portfolio. As foreign minister in the 1980s, he played an important role the creation of a single European market.

He offered his evidence to prosecutors last Thursday after 19 people had been arrested the day before in raids in and around Rome.

Two of those arrested were Mr Colombo's bodyguards, who were accused of placing orders for cocaine with a dealer three or four times a week.

Italy's news agency, Ansa, said Mr Colombo told prosecutors that the two men were innocent and that he was the true buyer.

He was quoted as saying: "I have not been a user for long - not more than a year, year and a half."

His lawyers criticised the leaking of his statement but did not challenge the accuracy of the report.

The admission, by itself, does not make him liable to prosecution because consumption of drugs in Italy is not a criminal offence. But it is a misdemeanor and his admission could mean he may have to appear before a judge to be reprimanded.

Cocaine has therapeutic applications as a local anaesthetic, to constrict blood vessels and raise blood pressure.

Its use in medicine today is largely confined to oral and plastic surgery.

Yesterday's disclosures are also embarrassing for the Vatican. Mr Colombo was a pillar of the Vatican-backed Christian Democrat party for more than 40 years and a strong advocate of family values.

In his statement Mr Colombo is reported to have acknowledged taking cocaine from an alleged pusher - one Giuseppe Martello - who is also accused of involvement in the supply of prostitutes.

Mr Colombo's alleged fellow customers included Serena Grandi, a star of Graffiante Desiderio (Clawing Desire), a porn film.

The latest revelations have also fuelled the debate over drugs in Italy. Mr Berlusconi's rightwing government is committed to introducing legislation which would abolish the distinction between hard and soft drugs and introduce stiff penalties for possession as well as trafficking.

Opponents have pounced on the fact that last week's arrest warrants named a junior minister, also a Christian Democrat, as another of Mr Martello's customers.

The investigation, codenamed Operation Cleopatra, involved more than a year of undercover work by Rome's detectives. In an intercepted telephone conversation, also leaked to the press, the owner of a restaurant in the centre of Rome is quoted passing on to Mr Martello the complaints of someone he identifies as a customer of them both.

The man had been provided with a prostitute at an agreed rate of €1,000 (£700). "She tells him, straight-off at the beginning '[No more than] one hour and a condom."