Britain detains suspected terrorists without charge for longer than many other comparable countries, human rights group Liberty has said.
Liberty suggests intercept evidence could be used
Currently the UK has a 28-day limit, but the government is considering extending that, with ministers suggesting it could be doubled to 56.
The Liberty survey was carried out by lawyers and academics in 15 countries.
It found Australia, which has a similar legal system, had the second longest limit - 12 days.
Last week Home Office Minister Tony McNulty said the government wanted to extend the limit, "probably" to 56 days.
Security Minister Lord West said "about 50" was the figure being talked about, but added safeguards would have to be in place to win over critics.
In France, terror suspects can be held for six days before the equivalent of a charge is made.
Meanwhile, in Germany, suspects must be seen by a judge within 48 hours but can be held without trial during the period of investigation. This must be reviewed by a judge at least every six months.
TERROR DETENTION LIMITS
France: Up to 72 hours without seeing a lawyer and four years in pre-trial detention
Germany: Must be seen by a judge within 48 hours but can be held without trial during investigation
Greece: Up to 12 months - 18 months in extraordinary cases
Italy: Up to 24 hours without seeing a lawyer
Norway: Up to 48 hours - a judge can increase this period
Spain: Up to 72 hours without a lawyer - can be increased to a maximum of 13 days
USA: The attorney general can detain foreign suspects but must start deportation proceedings within seven days. Suspects can be held for periods of six months
BBC home affairs correspondent Rory Maclean said it was difficult to compare legal systems, but Liberty had used the charge as an indicator of when the process moves from the police to the judiciary.
On that basis the 28-day limit in the UK was by far the longest, he said.
Liberty is calling for Britain to use alternative measures, including the use in court of intercept evidence, such as from phone taps.
It argues that better investigatory powers for police are an alternative to extending detention times.
Liberty director Shami Chakrabarti told BBC Radio 4's Today programme she would also back measures allowing for a suspect to be charged with a lesser offence while investigations for other related offences continued.
"With safeguards, I think it's perfectly proper to charge someone with a lower-level offence, like possessing explosive material or attending a terror training camp, while you continue to investigate a complex conspiracy to murder."
Attempts in 2005 to extend pre-charge detention to 90 days ended in Tony Blair's first Commons defeat as prime minister.
Instead, MPs voted to extend the period from the then limit of 14 days to 28 days.