Government safeguards used to defend ministers' calls to increase the period for which terror suspects can be held without trial were today dismissed as "meaningless".
MPs said the government's arguments for a 42-day detention period without charge period were a "charade" and dismissed appeals from home secretary Jacqui Smith.
Appearing before the home affairs select committee, Ms Smith argued the pre-charge detention period should be increased as the present 28-day limit could one day prove too limited.
Although she admitted no case has yet collapsed because of inadequate questioning time, Ms Smith told MPs there is "at least a possibility" that a terror suspect would be released in the future before sufficient evidence is obtained.
Under the government's proposed reforms, the home secretary would be able to approve detaining terror suspects for 42 days on a request from the director of public prosecutions and relevant chief constable.
Parliament would then have to approve this decision within 30 days.
Labour MP David Winnick challenged Ms Smith that the so-called safeguards are a "cosmetic exercise".
He was backed by Tory backbencher James Clappison, who said the parliamentary veto would be "meaningless" and it was "misleading to describe it as a safeguard".
Human rights group Liberty further warned parliamentary and judicial safeguards were "close to laughable".
Liberty director Shami Chakrabarti said: "The only 'consensus' is of opposition to extending the longest pre-charge detention in the western world.
"The home secretary wants an 'on-off button' to intern suspects - not in times of emergency but at moments of convenience."
Under questioning by the committee, Ms Smith confirmed critics' allegations that terror suspects could still be held beyond the current 28-day limit while parliament prepares to vote.
MPs also pointed out it would be difficult to debate the validity of an extension without prejudicing an ongoing investigation.
The government proposed the 42-day detention limit last week as a compromise measure after MPs showed little willingness to extend the current 28-day limit.
Even though it is below the 56- or 58-day originally mooted by ministers, Ms Smith said a 42-day detention period was still "likely to be adequate in the future".
Pressed on whether there was a need to extend the pre-charge detention limit, Ms Smith conceded only six respondents to the government's 71-strong consultation had "unequivocally" backed extension.
Despite scepticism from the Conservatives and Liberal Democrats, Ms Smith said she expected to win over a majority in the House of Commons.
Lib Dem home affairs spokesman Nick Clegg insisted, however, there is no case for reopening the debate on pre-charge detention.
Mr Clegg said: "Jacqui Smith gets full marks for her honesty in admitting there is no hard evidence in favour of extending detention without charge and that only a tiny minority of respondents to the government's consultation process support the move.
"Her problem is that the more we hear of the government's arguments, the less convincing they become."
The home affairs select committee is due to publish its report into pre-charge detention "shortly" and Ms Smith confirmed the government will introduce a bill soon after.