The British Home Office is considering setting up special anti-terror courts which would sit in secret to determine how long suspects should be detained without charge.
Under the plan, French-style judges would evaluate sensitive evidence, including currently inadmissible phone-tap evidence, to assemble a pre-trial case against terror suspects.
Earlier it emerged that Omar Bakri Mohammed, a radical cleric who faced possible charges in connection with inciting terrorism, has left Britain for Lebanon, as the Crown Prosecution Service considers whether to take action against him.
The cleric, who in an interview last week said that he would not inform the police if he knew bombers were planning an attack on Britain, insisted he would return to the UK next month.
Meanwhile a former minister and senior Blairite MP has criticised the government for its apparently panicked handling of initiatives to counter the threat posed by Islamist extremists.
John Denham, the Labour chairman of parliament's home affairs committee and a former Home Office minister, led cross-party criticism following suggestions that prominent Muslim clerics who have backed terror acts could be prosecuted for treason.
Mr Denham told the Financial Times he was concerned by the way senior government figures including Tony Blair had rushed out a number of controversial moves without prior consultation. He called for a return to the "measured approach" of past weeks.
"What is more worrying is the sense of slight panic that seems to be emanating from the government over the last few days," he said. "After the [London] bombings, there was a very sensible and measured approach recognising things needed to be done and discussed. The flurry of announcements over the last few days, many of which haven't been developed fully, gives the sense that the government is not fully in control of events and that's unfortunate."
His comments came as four men suspected of conspiring to murder passengers in the July 21 attempted attacks appeared in court for the first time on Monday.
Mr Blair caused controversy on Friday when he banned radical groups including Hizb ut Tahrir and widened the grounds for deportation of Islamist ex-tremists. The prime minister said he was prepared to amend the Human Rights Act if the courts opposed the government's proposals.
Home Office officials have since confirmed that Hizb ut Tahrir is not a terrorist group. Then, on Sunday, it emerged that Lord Goldsmith, the attorney-general, was discussing with crown prosecutors and police whether several prominent clerics could be charged with treason for recent comments supporting terrorism.
That caused a political furore on Monday and government insiders played down the likelihood of a treason charge, which has not been used for 60 years and would involve practical difficulties. More likely options included solicitation to murder, in-citement to racial hatred or withholding evidence of use to the police. The attorney-general's office said: "Until the evidence is considered, no decision will be taken on any charges."
Mr Denham said it was "surprising" that a treason charge had been suggested when it had never been used against members of the IRA. It was difficult to identify anything that the Islamist clerics were doing that was different to how IRA supporters had behaved.
The four men alleged to have been involved in last month's failed bomb plot were charged formally and re-manded in custody when they appeared at Bow Street Magistrates' Court sitting at the maximum security Belmarsh prison in London.
A fifth suspect, Hussain Osman, is being held in Rome awaiting an extradition hearing.
Separately at the Belmarsh court, Haroon Rashid Aswat, a 30-year-old British terrorism suspect, faced an application for extradition to the US on charges of trying to set up a terrorist training camp there.