Jacqui Smith has been warned by her department, the Home Office, that moves to lock up terror suspects for up to 42 days could provoke a backlash among Muslims.
The Home Secretary pressed ahead yesterday with moves to increase the detention period from 28 days – the longest in the West – despite opposition among MPs of all parties and civil liberties groups. She faces a struggle to force the legislation on to the statute book.
Publishing a new counter terrorism Bill, Ms Smith insisted the extra powers were essential in the light of the increasing complexity of terror plots against Britain. But research for the Home Office acknowledged that ministers would face problems in persuading Muslims that the move was justified.
An equality-impact assessment, published by the department, said that Muslims felt that the anti-terror legislation already in force discriminated against them. It noted: "Muslim groups said that pre-charge detention may risk information being forthcoming from members of the community in the future."
The research echoed the conclusions of focus groups of young Muslim men conducted on behalf of Liberty, a civil liberties group. The polling company ComRes found that most Muslims believed the 28-day maximum was already too long. They said: "There is a strong consensus that extending the limit would only serve to promote the extremists' cause, that it would do little to help tackle terrorism, that it would damage the UK's international reputation and that it would further erode community relations."
Ms Smith is mounting a concerted drive to win over Labour MPs hostile to the proposed 42-day limit, which is also strongly opposed by the Conservatives and Liberal Democrats. Party whips admit they face the prospect of defeat.
A survey by The Independent last month found that 38 Labour MPs – enough to overturn the Government's majority – were prepared to defy the Home Secretary. The issue of pre-charge detention led to Tony Blair's first defeat in the Commons in November 2005, when he sought a 90-day limit.
Ms Smith has promised that the 42-day power would only be used in "exceptional circumstances" and would be subject to judicial oversight and a parliamentary vote. David Davis, the shadow Home Secretary, said: "Her fixation with extending pre-charge detention risks serving as a recruiting sergeant for terrorism."
He added: "The Government has not been able to present a shred of evidence to justify extending pre-charge detention, and there is now a range of evidence pointing the other way."
Nick Clegg, the Liberal Democrat leader, said: "The obsession with 42 days is undermining, not supporting, the battle against terrorism."
The Bill also proposes a criminal offence of "communicating, publishing or eliciting" information about service personnel. Gathering details about members of the armed forces will carry up to 10 years' imprisonment if there is suspicion of a plot to place them in danger.
Other moves include allowing police to question terror suspects after they have been charged and closing a loophole which stops police from sharing fingerprints or DNA samples taken from terrorist suspects held under control orders.