Vast resources have been spent on counter-terrorism in Britain since the September 11 attacks.

High-profile buildings such as the Houses of Parliament and Scotland Yard have seen security walls erected and rigorous searches of visitors.

The Government has spent £56 million on mass decontamination units for use in the event of chemical, biological, radiological or nuclear attack, such as a "dirty bomb".

Another £132 million has gone to the fire service for search and rescue, £85 million to the NHS to cope with bioterrorism and £49 million to the Metropolitan Police's counter-terrorist work.

The Security Service, MI5, has already begun a recruitment campaign to increase its size by 50 per cent to 3,000 staff by 2008.

Last July, Chancellor Gordon Brown said spending on security of the UK was £950 million a year before the atrocities at the World Trade Centre and the Pentagon.

Now overall security spending will rise from £1.5 billion in 2004/05 to reach £2.1 billion by 2007/08.

The new Serious and Organised Crime Agency planned by the Government will also play an important role in tackling the links between organised crime and terrorism.

Although spending has increased massively, there have been comparatively few convictions of terrorists in the courts.

In all, 702 people were arrested under the Terrorism Act 2000 between September 11 2001, and the end of 2004.

Of those, 119 were charged with terror offences and a further 135 with other crimes under general criminal law.

Only 17 have been convicted under the Terrorism Act.

Generally, there is a lack of information about the arrests and subsequent court cases, leading the all-party Home Affairs Select Committee to express concern on April 5 this year, and call for better statistics.

There have also been a series of high-profile cases in which defendants accused of terror-related offences have been cleared or had cases dropped.

The Government has faced the difficult problem of balancing security requirements against human rights.

In December 2004, the House of Lords ruled the controversial internment powers rushed through Parliament in the weeks after September 11 were illegal.

The ruling led to the final ten foreign terror suspects detained without charge or trial at Belmarsh Prison under the powers for more than three years being released in March on new "control orders". Conditions include a night curfew, a ban using mobile phones and the internet and Home Office approval to meet people.

In March, Home Secretary Charles Clarke pledged a new anti-terror Bill in the following session of Parliament which would include a new offence of "acts preparatory to terrorism" allowing more suspected terrorists to be tried in the criminal courts.

But he has been criticised for refusing to allow phone tap evidence and other surveillance material to be made routinely admissible in the courts. Conservatives say such a move could lead to more terrorist convictions but some within the security services are believed to be opposed.