Sean O’Neill Crime and Security Editor The plan to detain terror suspects for 42 days has become so convoluted and bureaucratic that police fear it will be almost unworkable, senior sources have told The Times.

Counter-terror officials have watched the unravelling of the pre-charge detention scheme — through concessions designed to win the support of Labour dissidents — with increasing alarm.

Having studied the 19 pages of proposed amendments tabled this week by Jacqui Smith, the Home Secretary, senior detectives are unclear about how they would operate in the heat of a fast-moving emergency. They are concerned about the level of operational detail that would have to be shared with backbench MPs and lawyers and the ability of Parliament to vote in effect to end a police investigation.

During the past days senior sources have scrutinised the Government’s revised plans, and have chosen to share their concerns with The Times. Their fears include:

— Worries about the status, identity and role of the independent lawyer who will advise the Home Secretary on whether there is a sufficiently grave threat to justify the use of the 42-day power;

— A lack of clarity in the workings of the tripartite system of a judge, the independent adviser and the Director of Public Prosecutions — who together must approve extra detention. What if one of the three consistently opposes extended detention? Sir Ken Macdonald, QC, the current DPP, is a public opponent of 42 days;

— Concern over disclosing details of an investigation when explaining the need for further detention to the chairmen of the home affairs, human rights and intelligence committees;

— Fears that “parliamentary scrutiny” means that MPs have won the power to bring a police inquiry to an end.

“We firmly believe that the time will come, in the not too distant future, when we will need more than the current 28-day limit,” a counter-terrorism source said. “But if the proposals are enacted in this form then it will present the police with a bureaucratic nightmare. They are not the sort of thing you want to be dealing with in the middle of an investigation. Some of what is being proposed is very worrying because it amounts to a blurring of the lines between politics and operational policing.”

Another anti-terrorism source said that the proposals had become increasingly convoluted, and the circumstances that could trigger them more constrained.

“We seem to have moved from the concept of needing more time because the cases are more complex and bigger in scale, to more time being justified by the gravity of the threat to the public. The ‘exceptional circumstances’ that will need to be in place seem to be an entirely different rationale from where we started, which was something like ‘terrorism is by definition serious, it’s getting more complicated to investigate and we need to have the best possible chance to bring people to justice’. As for the parliamentary bit — does anyone really understand that or how it will work?”

Publicly, Scotland Yard has been attempting to steer a cautious course through the 42-day debate.

Having lobbied MPs unsuccessfully in 2005 for the power to hold suspects without charge for 90 days senior Metropolitan Police officers did not want to open themselves up a second time to the charge of becoming involved in politics. Sources emphasised that Scotland Yard did not press the Prime Minister for the 42-day proposal. Instead, Gordon Brown is understood to have summoned senior officers after last year’s attempted car bombings in London and Glasgow and said that he would be putting forward the proposal.

Scotland Yard came under pressure from No 10 to endorse Mr Brown’s scheme but attempted to keep its distance from the Government.

Sir Ian Blair, the Metropolitan Police Commissioner, appeared before the Commons Home Affairs Select Committee in October and emphasised that it was for Parliament to set the detention limit beyond the current 28 days.

Assistant Commissioner Bob Quick, the head of Special Operations, briefed MPs last month.

The Association of Chief Police Officers has acted as the main police supporter of the proposal by the Government.

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