Two human rights groups yesterday joined the opposition to government plans to extend the length of time terrorism suspects can be held before being charged.
In separate reports, Amnesty International and Justice both said there was no case for extending the limit of 28 days -- higher than any other EU state or the US -- for the detention of terrorism suspects.
Amnesty set out 10 reasons why extending precharge detention was unjustified while Justice said that laws in the US limiting detention to 48 hours have not stymied investigations into terrorism there.
The British government is thought to want to double the detention period to 56 days.
Amnesty said such a move would undermine basic human rights and lead to a deterioration in the relationship between the state and the country's 2 million Muslims.
"Locking up for two months without charge is no way for a liberal democracy to act. Extremists want to undermine our liberties and terrorism shows no respect for human rights," Amnesty International director Kate Allen said.
"The government needs to step up and show a principled opposition to terrorism, not take away people's rights," she said.
The 28-day maximum is already seven times higher than the maximum period suspects may be held without charge on suspicion of other serious crimes.
Amnesty said statements obtained from terrorism suspects held for a prolonged period could be inadmissible in court if conditions are considered to have been too harsh.
Justice released details of 10 high-profile terrorism cases in the US between 2002 and this year in which every suspect charged with a criminal offense was charged within 48 hours of being arrested.
"If the FBI can charge a terror suspect in 48 hours, why do UK police need more than 28 days?" said Eric Metcalfe, Justice's director of human rights policy and author of its report. "This report shows that complex terrorism cases can be investigated without the need for lengthy pre-charge detention or other exceptional measures."