There is a case for extending the 28-day limit on questioning suspected terrorists, the government's terror legislation watchdog has said.
A US-style National Security Council was backed by Lord Carlile
Lib Dem peer Lord Carlile of Berriew is due to report to the home secretary on whether the limit should be lengthened.
He told BBC One's Politics Show he had concluded that in a "small number" of cases, "a 28-day period between arrest and detention may be insufficient".
But Tory leader David Cameron said "no new evidence" supported an extension.
Lord Carlile gave Kafeel Ahmed, who died of his injuries after an alleged terrorist attack on Glasgow Airport, as an example of why police might need more time to question a suspect before bringing charges.
The peer said: "Had he survived, it is possible that time for interviewing him would have run out before he regained consciousness.
"So that's one example in which 28 days can be insufficient."
He added that cases which involved complex forensic analysis, or where alleged terrorists had carefully encrypted computer files, might also require suspects to be detained beyond the present limit.
He said: "My concern is not about the number of days. The number of days is a political decision, there's no logical answer as to how many days are ideal as a maximum.
"I'm concerned about the quality of the process and what I shall be emphasizing is increasing the judicial scrutiny over this process of detention so that those who are innocent are protected from arbitrariness by the state."
Lord Carlile suggested that a senior judge should be involved at an early stage to assess whether detention is justified.
He added that a new a US-style National Security Council, as proposed by Gordon Brown, was "an extremely good idea in principle".
But on Sky News' Sunday Live, Mr Cameron said the Conservatives would oppose any increase in the 28-day limit and insisted that Prime Minister Gordon Brown's position on the issue was confused.
The Tory leader added: "On the one hand to say this is a new chapter of British liberty, but he wants even longer to bang people up without charge or a trial.
"Totally muddled, totally incoherent."