It will stay that way after Charles Clarke, the Home Secretary, announced this week that using telephone intercepts in court would be too difficult, too dangerous and produce few extra convictions.

But proponents of change, including law lords, senior politicians and many police officers, say that the decision makes little sense because of the many other forms of surveillance that are already admissable in court.

Telephones on an internal network can be tapped and the material can be used. If one of the people taking part in a conversation on a public network, such as an under- cover officer or an informant, knows a tap is in operation, again the evidence can be used.

Tapes from bugs put in homes, businesses and vehicles are also admissible in court and have been used in IRA and drug trials. If the intercept is made by foreign police abroad it can also in theory be used in a British court.

In 2003 intercepts led to the seizure of 26 tonnes of drugs and 10 tonnes of tobacco, the detection of fraud and laundering operations worth £390 million and 1,680 arrests.

The United Kingdom will continue, with the Irish Republic, to be the only Western countries where conversations intercepted on a public network cannot be used as evidence. They can be used only for intelligence.

Warrants authorising intercepts are issued by senior ministers in cases of national security, serious crime, safeguarding the economy or some international cases. They can cover landlines, mobile telephones, pagers, text messages and e-mails.

The number of intercepts has been rising steadily: in 2003 there were 1,983 warrants in operation in mainland Britain, including a small number of letter intercepts. No figures are published for warrants issued for the Foreign and Commonwealth Office or Northern Ireland.

The call for intercepts to remain secret is led by the intelligence community, supported by some Customs and police investigators. They argue that revealing them would reveal the sophistication of electronic surveillance and provoke counter- measures.

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