The government's case for extending the length of time that suspected terrorists could be held without charge was dealt a double blow today.
Appearing before the home affairs select committee, which is investigating the government's counter-terrorism proposals, the former attorney general, Lord Goldsmith, said that he had seen "no evidence to go beyond 28 days".
Ken Macdonald, who is the director of public prosecutions and head of the Crown Prosecution Service, also undermined the case for an extension when he told the committee that the CPS was "satisfied" with the current limit.
While the home secretary, Jacqui Smith, has insisted that the government will seek a consensus on extending the limit, it is believed to favour increasing it by 30 days to 58 days.
Goldsmith said he strongly opposed the proposed extension of the detention limit from 14 days to 90 days, which was defeated in 2005. But he said he did agree with the compromise period of 28 days that was passed.
"There needs to be a limit to this," he said. "And while any limit is arbitrary I thought that we were really in the right place with the decision the Commons ultimately took.
"I was happy with the time limit that was decided but I wasn't happy with the time limit that was proposed."
Goldsmith said that no other members of the cabinet shared his concerns about 90 days to the same extent.
He repeated his past assertion that he would have resigned if it had gone through.
"If the 90-day proposal had come from the Commons, I would not have voted for that in the Lords and that would have had consequences for my position," he said.
He said that it was police arguments that had persuaded the government to increase the limit from 14 days but while attorney general he had not been persuaded of the case for a further extension.
Goldsmith warned that holding suspects for longer to "brow-beat" them would not prove productive and said the impact on communities of extending the limit was "a very important consideration".
"To keep someone in detention without charging them, surely you need to have reasonable suspicion, even if you can't prove it at that point, that they committed an offence," he said.
Macdonald said that only three cases had required holding a suspect without charge for more than 14 days and that the CPS had not made the case for an extension beyond 28 days.
"It seems to us 28 days has been effective and has provided us with powers, supervised by the courts, that have been useful to us," he said.
"We haven't had any cases that would require longer than that."
Macdonald also expressed his belief that it would be difficult to persuade a court of the reasonable suspicion required to hold a suspect longer than 28 days if there was insufficient evidence to charge them at that point.
The shadow home secretary, David Davis, said: "Neither the director of public prosecutions, nor the last attorney general, have seen the evidence to go beyond 28 days.
"Terrorism will be defeated by good intelligence, professional policing and the rigorous application of British justice, not by unnecessary incursions into the freedoms and rights that British subjects have had for centuries."
Nick Clegg, the favourite to be the next Liberal Democrat leader, said: "Lord Goldsmith has blown the government's cover.
"When their most senior law officer for much of the last 10 years says he is unpersuaded by the case to extend detention without charge then the hollowness of the government's case is there for all to see."