Q&A: Control orders
What are control orders and what part do they play in British anti-terrorism legislation?
The orders were introduced under 2005 anti-terrorism legislation. Ministers sign an order to place a terrorism suspect under close supervision that some say is similar to house arrest.
Why were the orders introduced?
The orders were introduced after the then Law Lords declared that the previous system of detaining foreign terrorism suspects without trial, or without prospect of deportation, breached human rights.
The government said it still needed a mechanism which would allow it to control the lives of some suspects whom it said it couldn't prosecute because of the rules over the use of secret intelligence in trials. Control orders were designed to restrict the movements of any kind of suspect, including British nationals.
How do control orders work?
The home secretary has the power to make two different types of control order.
The first type lasts for a year and includes strict conditions such as home curfews and bans on who a suspect can meet. The other form, which has never been used, would involve opting-out of some human rights laws to severely restrict the movements of an individual in a public emergency situation.
What's the practical effect on the suspect?
In practical terms, a control order prevents a suspect from having a normal life.
They are given a boundary around their home that they cannot cross.
They are not allowed to use phones, other than the one in their home. They lose their passport and can be banned from using public transport.
They are electronically tagged and need ministerial permission for all sorts of apparently mundane everyday events.
Critics say this system is akin to house arrest with no end - and that it punishes the family as well as restricting the suspect.
But security officials believe that control orders work where they have been used to prevent a known suspect from meeting with other extremists.
How many people are currently on control orders?
According to the most up to date figures December 2010, there are 8 control orders in force - all of them British.
Almost 50 people have been subject to the controls since the system was created.
Has the law developed?
The Law Lords (now the Supreme Court) have issued a string of important judgements on the future of the regime.
The judges have limited the time that someone can be forced to stay in their own home to 16 hours.
In 2007, the Law Lords rejected a claim that control orders amounted to a criminal punishment without a fair trial.
Then in 2009, the Lords set out new rules for the use of intelligence material after a judgement on secret evidence from the European Court of Human Rights. The judges said that some controlees had been denied a fair hearing because they did not even know the gist of the case against them.
They deserved, the Lords ruled, to know an "irreducible minimum" of the allegations.
Why was this so damaging?
It all comes down to what material the home secretary, on the advice of his security officials, is prepared to put in the public domain. A great deal of the material amassed against control order suspects is information gathered by MI5.
It may include telephone taps, transcripts of audio bugs, tip-offs from important informants or information from other intelligence agencies around the world - in fact anything that could be classed as useful information.
Officers then make an assessment about what the information means - and this helps them to target the people they think are the most dangerous.
Why can't these allegations be put to the suspect?
None of this is criminal evidence as the police would gather it. It's not the kind of information that the home secretary wants in the public domain because it could reveal how MI5 looks for people who threaten national security.
So, in these cases, the judgement meant ministers were faced with a dilemma. Do they provide more information on the allegations and risk compromising secret techniques? Or do they withdraw their case and let the individual go free.
So what happened?
Some cases have been allowed to fall. Three suspects had their control orders quashed after the government refused to put more information in the public domain. In the case of at least one other controlee, the home secretary simply revoked the order. But in other cases, a tense battle took place in secret hearings over what level of information should be made public.
Give us an example?
One controlee who spoke to the BBC last year put it this way. He said that he had been accused of meeting Islamist extremists.
But he didn't know who the government meant - and so he said he could not explain to the court whether or not he had done anything wrong - or was simply caught in the middle of something else. He claimed he had never knowingly met an extremist.
People like him want to know who they are accused of meeting, and when, so they can provide an alibi. But if the government gives this information away - does it then let other suspects know how officers work and who they are watching. Supporters of secrecy say the risk is too high.
So where did this leave the system?
The system teetered - but did not topple. Former Labour ministers said the system was an "essential tool for protecting the public from terrorism".
But following the general election, the Liberal Democrats wanted it scrapped. That led to the tense behind the scenes talks over introducing a new system between the coalition government partners.