The Home Secretary's proposals immediately came under fire from the Conservatives, Liberal Democrats and civil liberties groups. And Mr Clarke faced embarrassment after a draft letter to opposition parties was leaked suggesting he had private reservations over locking up suspects for up to 90 days.
The Government wants to rush the wide-ranging package, produced two months after bomb blasts killed 52 Tube and bus passengers in London, into law before Christmas. But the Home Secretary faces entrenched opposition to the plan to increase from 14 days to 90 days the period that terrorist suspects can be questioned.
Police have asked for the extra time to conduct complex investigations, but critics say the provision undermines Britain's tradition of civil liberties and could act as a recruiting sergeant for terrorists.
In a letter to his Tory and Liberal Democrat counterparts, Mr Clarke confirmed that the planned Anti-Terrorism Bill would extend the maximum period of detention from 14 days to three months. The extension of detention would have to be approved every week by a judge.
But in an earlier version of the letter, he said: "I think the case for some extension is clear, though I believe there is room for debate as to whether we should go as far as three months." The Home Office said: "The changes were made within his office after he had seen the draft."
But Mr Clarke looks certain to compromise over the 90-day proposal because it is opposed by the Tories and the Liberal Democrats. He also faces a battle over the proposed new offence, carrying up to five years' jail, of "glorifying, exalting or celebrating" terror attacks.
It will not be an offence to glorify events of more than 20 years earlier, except those specified by the Home Secretary. This category could include the Holocaust and IRA attacks in the 1970s. Shami Chakrabarti, the director of Liberty, said glorification was so broadly defined that the Bill would "make loose talk a serious criminal offence".
Mark Oaten, the Liberal Democrat home affairs spokesman, said the glorification offence and detention powers would require a "major rethink" to retain his party's support, because it "could be open to too wide an interpretation".
David Davis, the shadow Home Secretary, broadly welcomed the package, but said the Government had yet to make "a convincing case" for 90-day detention.
Massoud Shadjareh, of the Islamic Human Rights Commission, said: "These measures, coupled with faulty British intelligence, will increase the witch-hunt against Muslims similar to that conducted against the Irish community."
The draft Terrorism Bill contains a crackdown on extremist Islamic bookshops by drawing up an offence of "dissemination of terrorist publications". It strengthens the Home Secretary's powers to proscribe organisations that he believes glorify terrorism; Tony Blair has already indicated that he wants an ban on the Islamic organisations Hizb ut-Tahir and al-Muhajiroun.
Offences of "indirectly inciting terrorism", preparation of terrorist acts and undergoing training in terrorist techniques, such as attending al-Qa'ida camps, will also be created.
The Government is also considering allowing terror suspects to turn "supergrass", in return for shorter sentences.
* Terrorist suspects can be held for up to 90 days without charge
* New offence of "glorifying, exalting or celebrating" terrorism
* Crackdown on extremist Islamic bookshops
* Ban on inciting terrorism
* Outlawing organisations glorifying terrorism
* Banning attendance at terrorist training camps
* Anybody applying for citizenship must be "of good character"Reuse content