The Prime Minister told his monthly press conference that the police had made a "good and compelling case" for gaining extra time to investigate terrorist crimes in the wake of the London bombings in July. But Charles Clarke adopted a more conciliatory tone, saying he did not have an "absolute fixation" with the 90-day upper limit.
David Davis, the shadow Home Secretary, said: "The public expects, especially at this time of heightened terror, the Government to speak with one voice. The Prime Minister's aggressive stance seems rather at odds with the constructive approach of the opposition parties to achieve both the security and the liberty of the British public."
Although Mr Blair denied any split with Mr Clarke, he admitted there was a "debate" going on inside the Government over the 90-day limit, after it emerged that the Attorney General, Lord Goldsmith, has not yet endorsed the proposal.
The Terrorism Bill, to be published today, would allow the police to hold terrorist suspects for up to three months. But ministers may have to compromise to win the support of the Tories and Liberal Democrats, who oppose the proposed limit.
Insisting that he cared deeply about civil liberties, the Prime Minister said: "I'm not saying that whatever the police say, we have got to do it. If the police, charged with fighting terrorism in this country, say to me and MPs 'This is why we need it', and that case is a good and compelling case - as I find it is - then my duty is to do it, unless someone can come forward with a very good argument why their case is unsound."
He went on: "I don't agree that the police would simply bang up anybody they wanted to bang up. If [the police] are right, how can I responsibly refuse to do something that will protect the most basic civil liberty, which is the right to life?"
Mr Clarke insisted he supported the 90-day plan and dismissed as "utterly unwarranted" claims that it amounted to internment. But he told the Commons Home Affairs Select Committee he was prepared to seek all-party consensus on it: "I completely recognise there is a concern. Three months is not a God-given amount and that's why I indicated flexibility to deal with that in the proper way." In a further concession, the Home Secretary said he would consider a proposal that the new detention powers should be overseen by a High Court judge, rather than a district judge.
During fierce exchanges with the committee, Mr Clarke denied the Government was moving towards "a totalitarian Britain". He dismissed a claim by the Law Society that Cherie Blair, who has remarked that Palestinian suicide-bombers blow themselves up because they "feel they have got no hope", could fall foul of the new legislation.
He said: "I would categorically say that the remarks referred to will not be covered by this legislation. Analysis of why terrorism takes place is very important. But encouraging and glorifying is completely different."
MPs argued that opponents of the regimes in North Korea and Zimbabwe could be prosecuted under the new law even for advocating attacks on government buildings. Mr Clarke conceded that was possible, but argued that a "fantastic transformation" towards democracy over the past two decades meant political violence could never be justified. He said: "I cannot myself think of a situation in the world where violence would be justified to bring about change."
He suggested he was open to compromise on a contentious proposal to outlaw glorification of terrorism, which has already been toned down. Faced by accusations from MPs and civil rights groups that the proposed law was too broadly defined, he said: "I'm ready to have a discussion." In contrast, Mr Blair insisted this plan was not being watered down.
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