The government hopes its concessions will head off a Commons defeat
The government has still not done enough to protect individual liberty in its anti-terror plans, an influential committee of MPs and peers says.
Home Secretary Jacqui Smith unveiled a series of amendments earlier this week aimed at heading off a Commons defeat.
But in a new report the joint committee on human rights said the safeguards were "inadequate".
And plans to hold terror suspects for up to six weeks without charge would "almost certainly not be lawful".
Ms Smith told The Spectator she thought the government would win next week's crunch Commons vote on 42-day detention.
But she also stressed that defeat would not bring down the government, as some commentators have predicted.
"I think if it was turned into a vote of confidence there would be massive support of the government, I don't think it would be a problem," she told the magazine.
Ms Smith has unveiled a series of amendments to the Counter-Terrorism Bill aimed at winning over critics.
These include greater Parliamentary oversight and the stipulation that extra detention powers could only be used in the event of a "grave exceptional threat".
The government argues that the scale and complexity of terror plots mean police will inevitably need longer to hold suspects in the future.
This report takes paint-stripper to the government's claims that it is installing adequate safeguards
Chris Huhne Liberal Democrats
But Lib Dem, Conservative and up many Labour MPs are still thought to be planning to vote against the plans on civil rights grounds.
It had been thought as many as 50 Labour MPs would vote against the plans, but some are thought to have changed their minds after studying the amendments.
But a report by the joint committee on human rights published on Thursday said the amendments offered were "inadequate to protect individuals against the threat of arbitrary detention".
The committee said the description of a "grave exceptional threat" was not tight enough.
Committee chairman Labour MP Andrew Dismore said: "The government has talked of a major emergency, the 'nightmare scenario' of simultaneous plots across Britain or two 9/11s at once.
"Yet the amendments tabled by the government provide for possible events falling well short of that."
The report also said requiring the home secretary to declare publicly there was a serious enough emergency to justify the powers was not much of a safeguard without independent scrutiny.
And allowing Parliament to vote on the individual case within seven days - another concession - would make little difference as any debate would be "heavily circumscribed by the risk of prejudicing future trials".
It concluded: "No amount of additional parliamentary or judicial safeguards can render the proposal for a reserve power of 42 days' pre-charge detention compatible with the right to liberty in Article 5 of the ECHR (European Convention of Human Rights)."
For the Liberal Democrats, Chris Huhne said: "This report takes paint-stripper to the government's claims that it is installing adequate safeguards for the use of 42 days of detention without charge."
Later on BBC One's Question Time the Conservative former foreign secretary Lord Hurd said he the measure may get through the Commons, but he was "pretty sure" it would be thrown out when the Counter-Terrorism Bill reached the Lords.
Shami Chakrabarti, director of the pressure group Liberty, told the programme: "It's not justified, it's wrong in principle."
Of the government's amendments she added: "They are not concessions, nobody who doesn't want to be fooled is going to fooled by those are concessions... They are rubbish, let's not be conned."
But Foreign Secretary David Miliband said since the pre-charge detention period had been extended from 14 to 28 days, there had been three cases where people had been held for up to 27 days.
"It's right that we take out the insurance policy - this isn't a target that we are aiming for, 42 days, it's an insurance policy that we might need the 29th, the 30th or more days."
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