The House of Lords has begun a detailed debate of controversial plans to allow the house arrest of terror suspects.
The Lords are to debate several amendments to the bill
The committee stage debate will cover government and opposition amendments to the Prevention of Terrorism Bill.
Tony Blair has rejected a Tory offer to back the bill if he accepted a clause giving it a November expiry date.
It scraped through the Commons after ministers pledged to amend it in the Lords to switch control of house arrest orders from politicians to judges.
The government's majority was cut from 161 to 14 on one vote on the bill, after Labour backbenchers staged a rebellion on Monday.
Liberal Democrat leader Charles Kennedy conceded that if all his MPs and Tory colleagues had attended that vote, the measures could have been thrown out.
Opponents of the bill in the Lords, including Lib Dem and Tory peers, now hope to force more concessions from ministers.
As controversy over the proposals continues, campaign group Liberty has placed an advertisement in the Guardian and Independent newspapers publicising its petition against the bill.
The document, backed by hundreds of names, including several public figures and scores of legal experts, calls for an end to detention without trial and respect for the principles of justice and human rights.
The group opposes "control orders" outlined in the bill which, as well as placing British and foreign terrorism suspects under house arrest, could mean curfews, tagging or bans on telephone and internet use.
These would replace current powers to detain foreign suspects without trial, which the law lords have ruled against as a breach of human rights.
Shami Chakrabarti, director of Liberty, urged the two opposition parties to pull together and oppose "a thoroughly bad bill".
"The government has behaved appallingly in holding a revolver to Parliament's head in saying: 'You pass this in two weeks or the world will end' - that's not an acceptable way to treat Parliament," she said.
The Tories want judicial oversight of all control orders, not just house arrest.
The House of Lords Constitution Committee has also said the orders should be made by judges, not ministers, and any legislation should be subject to an annual review, and last for a maximum of five years.
Mr Howard said it would be "far better if the whole of the legislation was subject to a sunset clause so Parliament could consider it all in a proper way instead of it being ramrodded through".
Mr Blair said the house arrest powers were already going to be subject to a sunset clause because they were annually renewable.
The second, less stringent, type of control orders would be subject to a court appeal within 14 days and there would be a three-monthly report on their use by "an eminent and independent person".
"I believe [the new powers] are a proper balance between the civil liberties of the subject and the necessary national security of this country that I will not put at risk," said Mr Blair.
The Lib Dems say they will continue to push for more concessions and will not be forced to back a bad bill.
Mr Kennedy said he believed the government would have to shift to a "significant" degree if it was to get the bill on to the statute books.
His party is not happy with the "nature of the judicial involvement" in the issuing of control orders or the standard of evidence that has to be produced in the case of house arrest.
Home Secretary Charles Clarke will be taking part in a special edition of BBC's Question Time on Thursday, focusing on home affairs. Shadow home secretary David Davis and Liberal Democrat home affairs spokesman Mark Oaten are also taking part.