The 28-day limit for police to hold terror suspects without charge may well need to be extended, an influential committee of MPs says.
The police have backed a 90 day detention limit
But the Home Affairs Committee report warns any such move would require extra safeguards to be put in place.
It attacks the government for the way it put its argument for a 90-day limit, a plan thrown out by Labour rebels.
Committee chairman John Denham says evidence leading to detention without charge needs to be "compelling".
Home Office Minister Tony McNulty said he welcomed the committee's report, but not the "severity of any criticism".
He said the police had made it "very, very clear" that they would require up to a 90-day limit, which the government had accepted.
However, he said while the committee recognises "there is a new threat ... it then says without a substantive evidentiary base the case wasn't made for going beyond 28 days, which is really rather contradictory".
Ministers have made clear they feel there is still a need to go further than the 28-day compromise, which was agreed in November after Tony Blair suffered his first Commons defeat as prime minister.
In its report, the committee says no recent cases provide justification for a longer detention period.
But it adds: "The growing number of cases and the increase in suspects monitored by the police and security services make it entirely possible, and perhaps increasingly likely, that there will be cases that do provide that justification.
"We believe, therefore, that the 28-day limit may well prove inadequate in the future."
However, the MPs say there should be regular assessments to see if suspects could be released under supervision such as tagging or control orders and that all arrests should be subject to judicial supervision.
The report says such measures would have helped in cases such as the recent anti-terror raid in Forest Gate, east London.
It calls for a senior committee to be formed to keep the detention limit under review.
'Lack of care'
But it is highly critical of the roles played by the police and the government in the attempt to set a 90-day limit.
"On such a major issue, with very significant human rights implications, we would have expected the case made by the police to have been better developed."
The report adds that it was "unsatisfactory" that the prime minister and home secretary had not "critically challenged" the police's advice to assure themselves of the case that was being made.
It says a "lack of care" in presenting the case, rather than the breakdown of political consensus blamed by then Home Secretary Charles Clarke, was the main reason for the difficulties.
John Denham, Labour chairman of the committee, said: "Earlier arrest, which means longer detention, is serving an important new function in disrupting and preventing terrorism.
"However, on an issue like this, the trust and confidence of the public and the Muslim community specifically is absolutely crucial; we cannot afford divisive arguments."
But he added: "Any new legislation should not propose longer than 28 days detention unless the evidence is compelling."
However, one member of the committee has rejected the report's findings.
Labour MP David Winnick, who tabled the original 28-day compromise motion, warned that any extension could antagonise the Muslim community and there would have to be "really compelling evidence" for such a move.
"The police would have to show that holding detainees for longer than 28 days was absolutely necessary in fighting against terrorism - they have not produced that evidence," he told BBC News 24.
"No-one so far has been held for anywhere near the 28 days."
The Home Office said the timetable for the Terrorism Act 2006, including the proposal to extend the maximum period of detention pre-charge, had been accelerated with opposition party backing after the 7 July attacks last year.
He added: "The strong advice we received from the police, most notably from the country's most senior anti-terrorist police officer, was that terrorist investigations are now more complex and that the current maximum period of detention - 14 days - was no longer considered adequate."
The police had said there was a need to hold a small number of terrorist suspects for up to a maximum of 90 days.