Italy's largest mobile phone operator, TIM (Telecom Italia Mobile) SpA, has written to public prosecutors' offices throughout the country to warn that its system for intercepting phone calls is close to collapse.

"It's simple: the number of phone tap requests is constantly increasing and we have written to the prosecutors' offices to warn them that we are close to the limit and that we won't be able to cope with further requests," a TIM spokesman said.

Every Italian mobile phone operator is obliged by law to maintain the capacity to intercept calls on 5,000 handsets but the operators have found themselves in difficulty in the face of requests to intercept up to 7,000 phones, according to published reports. Taps must be authorised by a judge and normally last for 15 days, or 40 in the case of organised crime suspects.

The number of requests has been doubling every two years, Justice Minister Roberto Castelli warned recently in a newspaper interview, adding that it is far higher than in other European countries.

In Italy 72 people have their phones under surveillance for every 100,000 inhabitants, according to figures from Germany's Max Planck Institute. That compares with 62 in the Netherlands, 32 in Switzerland, nine in Austria and 0.5 in the US, the German criminological research institute said.

Asstel, the Association of Italian telecom operators, has responded to the technological and financial crisis by seeking a meeting with the Justice, Communications and Economy Ministries to discuss the upgrading of interception technologies and who should bear the cost.

Magistrates insist the phone taps are an essential instrument in the battle against crime and say investigators have to rely on them because of the difficulty in finding reliable witnesses.

Civil rights campaigners are concerned, however, that the investigative technique involves a massive violation of the right to privacy. "We must switch off this Big Brother which is invading citizens' lives," said Paolo Cento, a lawmaker for the opposition Greens Party.