Imprisoning terrorist suspects without charge for up to three months could breach human rights law, the Government's terror watchdog has warned.

Lord Carlile of Berriew dealt another damaging blow to the contentious plans - which are already under fire from MPs of all parties, senior judges and human rights groups - by raising fresh doubts over the legality of the plans. His remarks followed a unsuccessful attempt by the Government to argue that the proposals in the Terrorism Bill, published yesterday, were not out of step with other Western nations. A Foreign Office dossier showed that British police were being offered wider powers to interrogate suspects than is allowed in any comparable country.

The Bill sets out a range of proposals to combat terrorism in the wake of the London bomb attacks on 7 July. It outlaws the "encouragement" or "glorification" of terrorism, as well as creating offences of "preparing a terrorist attack" and "receiving training in terrorist techniques".

The Government will face a struggle to push through its plan to increase the time suspects can be held from 14 to 90 days.

In the face of accusations that it plans "internment by the back door", the Bill looks certain to meet fierce opposition in the House of Lords. The Attorney General, Lord Goldsmith, has already said he does not believe the Government has made the case for extending the time limit.

Tony Blair told MPs there was a "compelling argument" behind extending detention. It has been proposed by the police who argue they could require extra time to prepare for complex terrorist prosecutions.

Lord Carlile acknowledged that past investigations into terror networks had collapsed because police had needed more time to investigate. But he called for a much more robust judicial oversight of the detention plans. He said: "A more searching system is required to reflect the seriousness of the state holding someone in high-security custody without charge for as long as three months. I question whether what is proposed in the Bill would be proof to challenge under the Human Rights Act, given the length of extended detention envisaged."

In response, Hazel Blears, the Home Office minister, insisted the Government was certain the legislation was compatible with human rights law. She added: "It is right that people question and probe these issues but the three-month period is what the police and security service say is necessary."

Lord Carlile, the Government's independent reviewer of counter-terrorism laws, also voiced "real concern" about the detention of nine suspected terrorists pending deportation to Algeria or Jordan. He said the men, formerly known as the "Belmarsh detainees" who were later made the subject of control orders had, in effect, had their detention without charge reinstated when they were detained for deportation in August.

In further criticism, he said a proposed new offence of undergoing or providing terrorist training may be "more extensive than required" , warning it could criminalise undercover journalists. And he said plans to give police powers to close mosques needed "careful examination".

In August, Tony Blair ordered the Foreign Office to produce a dossier on anti-terrorism legislation overseas to demonstrate Britain was not out of step with similar countries. Publishing the document yesterday, officials said they wanted to contribute to the debate by showing the updating of anti-terrorism laws in response to the increased threats facing the world.

Officials acknowledged none of the countries surveyed had the 90-day detention without charge proposed in Britain. But one said: "The difference in the UK is that, once the 14-day period is exceeded, the barrier comes down and the police can no longer question somebody once they have been charged.

"That is not the case in France or Spain where the person leading the investigation is an investigating magistrate. It is very difficult to make comparisons because the systems are different."

Opposition MPs and human rights campaigners denounced the Foreign Office dossier as an own goal. David Davis, the shadow Home Secretary, said: " All it shows is that the case for detention without trial for 90 days still has not been made.

"If the Government wants to look abroad they really would do far better to follow the good and up to date example of our international partners by actually deporting extremists and allowing the use of intercept evidence in terror trials."

Mark Oaten the, Liberal Democrat home affairs spokesman, said: "Where other countries hold suspects for long periods, there are safeguards in the form of an independent judge who decides if there is a case to answer. Under the Government's plans, judges will simply rubber-stamp any police request for more time."

Shami Chakrabarti, director of the civil rights group Liberty, said the detention plans amounted to internment. She said: "Things have come to a pretty pass when the country that once defined justice for the rest of world seeks to win a race to the bottom in fair trial standards."

Stephen Jakobi, director of Fair Trials Abroad, said: "We are all swimming in the same direction, away from liberty."

Labour left-wingers also joined the attack. Bob Marshall-Andrews, a QC, said: "We condemn this legislation as an unnecessary and largely unworkable attack on civil liberties. The provisions for imprisonment without charge will be counter-productive and an incitement to terrorism.

John McDonnell, who chairs the Campaign Group of Labour MPs, added: " This is an unacceptable undermining of civil liberties in the New Labour tradition of knee-jerk legislation. We need to concentrate on improving and reforming the intelligence services and policing on the ground. We all want increased security but we cannot sacrifice essential civil liberties that have been won over generations."

Country by Country

BRITAIN

Powers to hold terror suspects

Currently suspects can be held for up to 14 days without charge. The Government wants to increase that to a maximum of 90 days, subject to judicial approval every week after the initial fortnight

Powers to expel terror suspects

The Government proposes deporting foreign terror suspects to countries that give a formal guarantee they will not torture or mistreat individuals. Such a promise has been extracted from Jordan and the Home Office hopes to sign a deal with Algeria within months

AUSTRALIA

Powers to hold terror suspects

Suspects can be held for four hours, which can be increased to 24 hours on application to a magistrate. After that period, suspects are charged or released. The Australian Security Intelligence Organisation can hold suspects for up to 14 days under a warrant issued by a federal judge

Powers to expel terror suspects

Tough border controls mean Australia deports only 100 to 200 people a year. The country has ratified international human rights conventions and will not deport people if the countries to which they would be sent cannot give assurances that they will not torture or mistreat them

CANADA

Powers to hold terror suspects

Terror suspects can be held for a maximum of 24 hours before they must go before a federal court judge. There is no maximum time limit on detentions, but a judge must be satisfied that they are being held lawfully

Powers to expel terror suspects

Foreign nationals can be deported on suspicion of terrorism but must first come before an independent board. If the suspect's home country presents a human rights risk, it is up to the board to determine whether or not this is greater than the security risk to Canada

FRANCE

Powers to hold terror suspects

Suspects can be held for 48 hours initially, which can be extended by two further periods of 24 hours - four days in total. Under the French system of investigative magistrates, suspects can be held and questioned after they are charged for up to four years before their case is brought to trial

Powers to expel terror suspects

Foreign citizens can be expelled if they pose a threat to public order or on urgent security grounds. Those with long-term residence permits are liable to expulsion but those granted political asylum cannot be expelled

GERMANY

Powers to hold terror suspects

Suspects must be brought before a judge within 48 hours of arrest. They can be remanded in custody while the criminal investigation is under way, with detention reviewed by a judge at least every six months

Powers to expel terror suspects

People can be deported for "hate preaching" under a law that came into force at the start of the year. The Government can also limit the political activities of foreigners. Where expulsion would breach human rights law, suspects can be put under supervision orders

GREECE

Powers to hold terror suspects

Arrested suspects must be brought before a public prosecutor within 24 hours. They can be held for up to 18 months under extraordinary circumstances

Powers to expel terror suspects

Non-Greeks can be deported if they have received any prison sentence of at least one year for treason, crimes against the form of government or drugs

ITALY

Powers to hold terror suspects

Under a new decree passsed in July, suspects can be detained for 24 hours before being brought before a magistrate; the former maximum was 12 hours

Powers to expel terror suspects

Those suspected of promoting terrorism can be deported on the order of a police chief, whereas - prior to July - the decision was with the courts. The deportee can appeal against the deportation order but only once he is in the country to which he has been deported

NORWAY

Powers to hold terror suspects

Suspects can be detained for a maximum of 48 hours. Judges can grant further blocks of detention, usually in periods of one week. In theory, suspects can be detained indefinitely, although tough legal hurdles, in effect, limit the ability of authorities to hold individuals for lengthy periods

Powers to expel terror suspects

Can deport foreign nationals but cannot send foreign nationals to an area where they are in danger of being persecuted

SPAIN

Powers to hold terror suspects

A suspect can be held for 72 hours, extendable for two days after arrest before the magistrate decides whether to commence proceedings. Further extensions take the total time suspects can be held to 13 days. Once charged, they can be held for up to two years or, rarely, four years before trial

Powers to expel terror suspects

Suspects can be held up to 40 days pending deportation if they have participated in activities prejudicial to the state. Proceedings are halted if the individual claims asylum and only recommenced if the claim is deemed unfounded. Does not allow deportation to a country that allows the death penalty

SWEDEN

Powers to hold terror suspects

Suspects can be held for a maximum of four days without going before a judge, though most cases are dealt with within 24 hours. Once a detention order is made by a judge, it must be renewed every two weeks but, theoretically, there is no limit to the number of times that can be done

Powers to expel terror suspects

Legislation allows foreign nationals to be deported for reasons of national security. Any expulsion order will not be enforced where the person faces a risk of the death penalty, torture or persecution

UNITED STATES

Powers to hold terror suspects

Varies from state to state, each one having its own legal system

Powers to expel terror suspects

The Patriot Act allows people associated with terrorist organisations to be denied entry to the US or deported. The Act also gives the attorney general powers to detain any foreigners who are suspected of terrorism. American citizenship can also be revoked