Only a 'grave threat' would trigger 42-day detention, say ministers

New powers to hold terror suspects for up to 42 days without charge would be triggered only by a "grave and exceptional" threat akin to the 7 July bombings in London, ministers said yesterday as they moved to defuse a potentially devastating revolt by Labour MPs.

Publishing 46 amendments to the Counter-Terrorism Bill, ministers insisted the raft of concessions would ensure that the contentious powers were used only in the most extreme circumstances and would strengthen the right of MPs to veto the emergency measures.

But although Labour rebels appeared to have been won over, opposition parties accused ministers of attempting to deceive Parliament, while civil liberties groups dismissed the amendments as "a con".

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Jacqui Smith, the Home Secretary, was scrambling last night to placate backbenchers who threatened to inflict a humiliating defeat on Gordon Brown over the proposals.

Amendments formally laid yesterday mean the Home Secretary would have to be satisfied that Britain faced a "grave and exceptional terrorist threat" before extending the current 28-day limit on detention without charge. They spell out that there must be a threat of a serious loss of human life, serious damage to human welfare or serious damage to national security before the 42-day limit could be imposed.

Downing Street and the Home Office said it would require a crisis similar to the 7/7 bombings in 2005, when 52 commuters died, before the power could be used. Other concessions include new guarantees that Parliament will have a vote on any extension of detention powers within seven days of them being triggered. The police would also only be able to apply for the emergency powers for 30 days, rather than 60. The chairmen of three powerful parliamentary committees would also have to be given classified briefings on the reasons behind the moves.

Yesterday, some influential figures on the Labour backbenches swung behind the Bill. Labour left-wingers conceded the number of hard-core rebels was down to between 25 and 30 MPs.

Ms Smith appears to have taken some of the heat out of the backbench rebellion after winning praise for her conciliatory speech at Monday's meeting of the Parliamentary Labour Party. One MP said: "She gave a very sober and assured speech. You could sense the respect growing for her. She treated us like grown-ups and didn't try to give us any old blarney."

Keith Vaz, chairman of the Commons home affairs committee, pledged his backing for the Bill. He said: "The involvement of Parliament at an earlier stage, the clarification of an extraordinary circumstance and the involvement of the judiciary along with measures announced today to work with ethnic minority communities preventively, have ensured that the 42-day detention period will not encroach on our civil liberties."

But David Davis, the shadow Home Secretary, said: "These amendments are a deception. The Home Secretary's power to extend the period of detention without charge to 42 days remains as wide as before... These amendments are a politically driven attempt to deceive Parliament."

The four key concessions

* The Home Secretary would have to be satisfied that a "grave, exceptional terrorist threat" existed before authorising an extension to the current 28-day limit on detention without charge. Ministers insist that this means the power would be triggered only in the most extreme circumstances. But critics say the definition is still too widely drawn.

* Parliament gets an earlier chance to debate the emergency powers, with a vote on the issue guaranteed after seven days rather than the 30 originally planned. Parliament would be recalled if necessary. But critics say MPs would have to take the Government's word on trust and would be deprived of much of the relevant information for legal reasons.

* Powers to hold terror suspects for up to 42 days could be applied for only by police over a 30-day, rather than a 60-day, period, stressing the emergency, short-term nature of the measure. But critics say it does not alter the principle.

* Three powerful committee chairmen – the heads of the home affairs, human rights and intelligence and security committees – would be briefed on the reasons for the move. But critics point out that they would not have a veto.