Since the 11 September attacks hundreds of people have been arrested in the UK under anti-terror laws, but only a handful convicted. Security forces have been accused by some of heavy-handedness. But there's nothing new about this pattern when policing against terror.
Many high-profile terror arrests do not lead to charges
Between the New York attacks and last month, there have been 561 arrests in the UK under the Terrorism Act. But up to the end of January, only 98 of these had faced charges under this legislation, leading to six convictions.
For some campaigners, this disparity between the number of people arrested and those who eventually face charges is worrying.
"There is clear evidence of disquiet in the Muslim community and a belief that they're being disproportionately targeted," says Barry Hugill of civil liberties campaigners, Liberty.
"When so many people are taken in for questioning and so few are convicted, it leads many to question the intelligence behind the raids."
As an example, a few days before this week's anti-terror raids, it emerged that four people arrested as terror suspects before Christmas had had the charges against them dropped.
Terror arrests in the early 1990s also led to few charges
Whether this pattern of many arrests and few convictions is good or bad can be debated - but it is certainly not a new or uniquely anti-Islamic phenomenon.
In the early 1990s, when Irish republican and Loyalist terror groups were the main focus of arrests, there were similarly low rates of charges.
In 1990 there were 193 detentions, which resulted in 28 charges. And in 1991 there were 153 detentions leading to only seven charges. In 1992, there were 160 detentions and 35 charges and in 1993 there were 152 detentions and 32 charges.
As an average over this period, it meant that only about one in six of those arrested faced charges.
This could be interpreted as a sign that intelligence-led raids are difficult to convert into prosecutions. It could be argued that the urgency of guarding against terror means it is worth risking mistakes. But it could also be argued that the authorities are unjustly casting their net too widely.
There are fears that innocent Muslims will feel under suspicion
There are some contentious differences in the current reaction to the threat of terror.
In the early 1990s, there were an average of about six people a year "excluded" from the country.
But under the current Anti-Terrorism Crime and Security Act, foreign nationals who cannot be deported can be detained indefinitely without charges being brought against them.
If these detainees can find another country in which to stay, they can leave Britain and go there.
At present there are 13 people held under these regulations, eight of whom have been detained without charge since December 2001. The most recent detention under these powers was in October 2003.
Liberty says that this is Britain's "Guantanamo Bay" - and that it is a "violation of human rights".
But the Home Office rejects this, saying that public safety is paramount and that the detentions are necessary.
There have been complaints about detentions without charges
"The Home Secretary's decisions to detain these individuals were made on the basis of detailed and compelling evidence," said a spokesperson.
The Home Office also warns against using the number of charges brought as a way of assessing the current impact of anti-terrorist legislation.
"It is a mistake to try and measure the 'success' or 'failure' of the Terrorism Act 2000 by looking at statistics," says a spokesperson.
Even though those arrested might not face charges under anti-terror laws, they may still face charges on other serious offences.
"The Terrorism Act is not just about arrests and convictions. It contains many wider measures - such as the proscription of international terrorist organisations - which have an important deterrent and disruptive effect to prevent terrorists from operating in the first place."