The arrest of a dozen men in a series of anti-terrorism raids raises questions about the level of security in the UK. BBC News Online looks at how the authorities are responding to the threat from terror within Britain's borders.
What is the scale of the police and security services' anti-terrorism operation in the UK?
The Security Services will treble in size within three years in response to terrorism from al-Qaeda and groups linked to it.
There is a similar expansion going on in the police Special Branch and Anti Terrorist Branch - the other arm of UK counter terrorism.
Their priority is to penetrate and obtain intelligence from inside organisations which pose a threat to the safety of the UK.
Have arrests under the Terrorism Act led to people being charged?
There have been 600 arrests in the UK under terrorism laws since September 11, 2001.
A total of 90 people have been charged but only around a dozen convicted so far.
But many trials have yet to take place and the true picture will only start to emerge once those trials have been completed.
When police carry out a terrorist operation they will arrest many people who may be on the fringes of the activity.
They also have to follow up known associates of suspects.
These people will be released if there is no evidence of their involvement.
What are the criticisms of the Terrorism Act?
The Terrorist Act is criticised as a kind of vacuuming operation.
Muslim communities feels it runs the risk of branding them all as terrorists, rather than a minority of individuals.
The most pointed criticism is of the law which allows foreign nationals to be held without charge.
That is likely to be changed by the government by 2006.
How does the government defend it?
The government - like all democracies - struggles to deal with terrorism within its normal laws.
It was difficult with IRA terrorism when all sorts of special measures - such as trials by judge not jury - were taken.
It is the same now with Islamic militants.
Governments will always face accusations of draconian measures disproportionate to the threat.
But ministers says there is a new threat which can only be tackled by new means.
What is the impact on the Muslim community?
Muslim communities are in a very difficult and exposed position.
Many feel they are victims of greater discrimination since September 11.