The police and intelligence services are calling on the Government to drop plans to disconnect persistent internet pirates because they fear that this would make it harder to track criminals online.

Lord Mandelson, the Business Secretary, has vowed to use the Government’s forthcoming Digital Economy Bill to introduce new measures to fight illegal file-sharing of music and films. He has also proposed that persistent pirates should have their internet connections suspended temporarily.

But The Times understands that both the security services and police are concerned about the plans, believing that threatening to cut off pirates will increase the likelihood that they will escape detection by turning to encryption.

Law enforcement groups, which include the Serious and Organised Crime Agency (Soca) and the Metropolitan Police’s e-crime unit, believe that more encryption will increase the costs and workload for those attempting to monitor internet traffic. One official said: “It will make prosecution harder because it increases the workload significantly.”

A source involved in drafting the Bill said that the intelligence agencies, MI5 and MI6, had also voiced concerns about disconnection. “The spooks hate it,” the source said. “They think it is only going to make monitoring more difficult.”

Enforcement groups are also unhappy that the Government’s change of plans has left them little time to draw up a response. Lord Mandelson’s intervention came two months after the Government’s Digital Britain report, published in June, failed to back disconnection. Instead, it proposed giving Ofcom, the media watchdog, powers to direct internet service providers to block pirate websites or “throttle” connection speeds.

It is understood that the Digital Economy Bill will specify a list of technical measures that can be deployed against illegal file-sharers, but it is not yet clear whether account suspension will be included.

The music industry, which claims that it loses £200 million a year to piracy, is desperate for the Government to adopt the suspension plans. It has mounted a lobbying effort and believes that Lord Mandelson will follow through on his proposals.

However, some industry figures believe that account suspension is a “poison pill” that will have to be jettisoned to get any measures through Parliament in what will be a tight legislative timetable before next year’s election.

Internet service providers such as BT and Carphone Warehouse have said that introducing any technical measures would increase the cost of broadband connections by about £2 a month. Consumer Focus, the watchdog, has also criticised the plans, which it said would violate customers’ rights.

A YouGov poll released yesterday suggested that the public are strongly against the proposals, with nearly 70 per cent saying that someone suspected of illegal downloading should have a right to a trial in court before restrictions on internet use were imposed. Only 16 per cent are in favour of the current plans.

The Government said that any measures would also be backed by a tribunal that would give those caught illegally sharing files the right of appeal.

The film industry, which puts its losses at more than £500 million a year, believes that slowing connections would be enough of a deterrent because of the time it would take to download large film files.

Bob Pisano, the president of the Motion Picture Association, flew to London last week to meet Lord Puttnam, the film-maker, who is expected to be a key voice in building support for the plans.

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