UK current legislation includes the Terrorism Act 2000, enacted to harmonise the separate laws covering Britain and Northern Ireland.
544 people have been arrested under the Act, but only 98 charged with offences under the Act. A few of those arrested under the Act have been charged with other offences.
This ratio of many arrests - and detentions - to few convictions is unusual. Civil rights lawyers have accused the authorities of using the Act simply to go fishing for wrongdoing among those they suspect but against whom they have little clear evidence.
Seventeen foreign nationals have been held since 2001 under the emergency powers allowed by the Anti-Terrorism and Security Act 2001. These people can be held indefinitely without charge in the high-security Belmarsh prison.
People who defend the government using these laws say that they reflect the government's sense of urgency to thwart an attack on Britain.
Recently Home Secretary David Blunkett announced some new measures he would like to see, including the right to use certain types of evidence previously inadmissible in court - such as phone tapping - to get convictions on terrorism charges.
He floated these ideas, a Home Office spokesman said, in order to "take the temperature of the country", by asking them where the balance lies between security and the defence of civil liberties.
Of course, terrorism is a real threat. But an atmosphere is being created in public debate now to get people to accept infringement of civil liberties. We are being encouraged to believe that curtailment of our legal rights - for we are all subject to these laws - is as inevitable as the terrorist attacks that the papers, since the Madrid bombings, are telling us to expect any day now.
The left, people who campaign, who protest, need to be champions of freedom, and not complacent about the introduction of more and more arbitrary or discretionary powers for the authorities.
In the first place, we cannot trust the state to be competent or honest in dealing with groups such as al-Qaida - who are the enemies of the left. Second, we can be sure that the state would like to curtail our freedoms when they can, and we must not sit by while they arm themselves with the legal weapons to do it or create an atmosphere where the population is told simply to trust the powers-that-be.