LONDON, (UPI) -- Controversial anti-terror laws came into force across Britain Thursday, to the dismay of civil liberties campaigners and Muslim groups who warned of potential legal challenges and a rise in extremism.

Human rights group Liberty cautioned that the speech offenses and bans on extreme political parties contained in the act would make Britain less safe by silencing dissent and alienating minorities.

Meanwhile, the Muslim Council of Britain urged the government to exercise "maximum restraint" in applying the new measures, and warned it would take legal action if ministers attempted to criminalize non-violent organizations.

The government is already battling to save anti-terror measures enacted last year; a high court judge ruled Wednesday that the so-called control orders introduced under the Prevention of Terrorism Act 2005 breached human rights law.

The judge said that the orders, under which terror suspects can be placed under restrictions ranging from curfews to house arrest without charge or trial, were "conspicuously unfair" and a violation of individuals' rights. The Home Office said it would appeal the ruling.

The control orders were introduced to replace previous powers to detain suspects without charge -- enacted as emergency legislation following the Sept. 11 attacks in 2001 -- which were found to be unlawful by Britain's highest court in December 2004. Twelve people are currently thought to be subject to the orders, several of whom had previously been detained at Belmarsh prison.

The government will likely face similar challenges over the Terrorism Act 2006, enacted only after a lengthy parliamentary battle. The controversy centers on two measures -- a new offense of "glorification of terrorism" and wider powers of proscription so that extreme but non-violent political organizations can be banned.

Critics say the glorification offense is so vague that it could criminalize legitimate protest. Under British law, terrorism is defined as violence against persons or property intended to influence a government; potentially, protesters calling for the overthrow of oppressive regimes could be caught under the legislation.

The offense drew stiff opposition in the House of Lords -- Parliament's unelected chamber -- which threw it out five times before finally passing it in March. Conservative and Liberal Democrat members of the elected House of Commons also voted against it, saying it was already adequately covered by existing legislation such as incitement to terrorism, to violence or to murder.

The bill was drawn up in the wake of the July 7 bombings, which killed 52 people in four coordinated suicide attacks on London's transport network.

Following the attacks, Prime Minister Tony Blair pledged to take action against so-called "preachers of hate," insisting "the rules of the game have changed."

However he drew criticism for suggesting the glorification offense was needed to prosecute protesters who, at a London demonstration against satirical cartoons of the Prophet Mohammed, waved placards calling for the killing of those who insulted Islam and threatened a repeat of July 7. Such acts were clear offenses under existing law, parliamentarians said.

The government also plans to use its new proscription powers to ban extremist, though not necessarily violent, organizations. It has already singled out Hizb ut Tahrir, a political party which advocates the establishment of an Islamic caliphate through non-violent means, for such a ban. Critics say, however, that criminalizing such groups will simply send them underground and fuel extremism.

Hizb ut Tahrir told United Press International last year that it would fight any attempted ban in the courts; Thursday, the Muslim Council of Britain also threatened legal action.

"The government's attempt to criminalize non-violent organizations, groups and individuals for supporting legitimate causes around the world and expressing political opinion will result in a loss of trust between the Muslim community and the government," the MCB said.

"The ramifications of this are serious, potentially putting us in more danger than we face today, by dividing communities and alienating those who we must work with in order to defeat terrorism."

MCB Secretary-General Sir Iqbal Sacranie added: "The fact that these laws are based upon a number of false premises and an unacceptably vague definition of terrorism makes them a recipe for disaster as well as a huge blow to our freedoms."

The human rights group Liberty, which like the MCB campaigned vigorously against certain parts of the bill, said it was deeply concerned that the legislation's silencing of dissent would lead to a growth in extremism.

"These new powers make us not only less free, we are also less safe when we drive dissent underground and alienate minorities," said Policy Director Gareth Crossman. "Swept up in this new anti-terror safety net could be those who protest against dictators like Zimbabwe's Mugabe or North Korean dissidents."

The act also contains relatively uncontested measures including new offenses of undertaking terrorism training, preparation or planning of a terrorist act and disseminating terrorist publications.

Police powers to hold terror suspects without charge for up to 28 days are still undergoing consultation and will be implemented at a later date. The government originally proposed an increase to 90 days from the current 14, though this was defeated after a rebellion of Labor parliamentarians.

The enactment of the legislation does not signal an end to the government's difficulties. Ministers now face the prospect of damaging court battles over a whole raft of measures, from both 2005 and 2006.

The problem, Lord Carlisle, the government's independent reviewer of anti-terror legislation, told the BBC Thursday, was that the 2001, 2005 and 2006 terrorism acts had all been rushed in, and therefore were likely to prove flawed.

"They have been enacted rather hastily, and one tends to legislate in haste and repent at leisure," he said.

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