There will have to be a “proper debate” in the country and in the House of Commons before the 28-day detention limit for terrorist suspects could be extended, the Government said.

Geoff Hoon, the Chief Whip, said he wanted a “national discussion” on fresh proposals to increase the time that terror suspects could be held without charge.

But Shami Chakrabati, director of human rights group Liberty, claimed that Britain could be heading for a state of “permanent emergency” and there could only be an extension to the limit if policing was being brought to a “standstill” by multiple plots.

Both were speaking ahead of an appearance by Jacqui Smith, the Home Secretary, before the Home Affairs Select Committee today. She is expected to be questioned about time limits for detention without charge.

Sir Ian Blair, Britain’s most senior police officer, has said that the detention limit should be extended amid a “mounting” number of plots. The Metropolitan Police Commissioner told the committee that a precharge period “somewhere between” 50 and 90 days was needed. He said the worst time to debate an extension would be “in the aftermath of an atrocity”.

Keith Vaz, Labour chairman of the select committee, told the BBC he feared that detention powers could “disproportionately affect” the Muslim community. He told the Radio 4 The World This Weekend: “The worry about this is that we then stigmatise whole communities and in my view that is the road to ruin.”

Mr Hoon told ITV1’s The Sunday Edition: “If the police and security services were calling for a extension by a specific number of days, I believe that there would have to be a proper debate in the country and in Parliament.”

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