Q&A: TPims explained
A terror suspect who has gone missing after changing into a burka at a west London mosque was subject to an order designed to restrict his movements and activities.
As police hunt for 27-year-old Mohammed Ahmed Mohamed, we look at this order, otherwise known as a TPim, to find out what it involves and what people think of it.
What are TPims?
They are Terrorism Prevention and Investigation Measures, to give them their proper name. They are placed on terror suspects - who officials decide can neither be charged nor deported - by the home secretary.
The home secretary can consider putting a TPim in place after an MI5 assessment of the suspect and must "reasonably believe" he or she is involved in terrorist-related activities.
The measures include electronic tagging, reporting regularly to the police and facing "tightly defined exclusion from particular places and the prevention of travel overseas". A suspect must live at home and stay there overnight - possibly for up to 10 hours. However, they can apply to the courts to stay elsewhere. The suspect is allowed to use a mobile phone and the internet, to work and study, subject to conditions.
TPims expire after a maximum of two years unless new evidence emerges of involvement in terrorism. Breach of a TPim can lead to jail.
How many people are subject to them?
As of August, nine men - eight of them British - were under TPim surveillance.
In 2012, TPims' first year in use, 10 men - nine of them British nationals - were under TPims. Four of them had previously been charged with terrorism offences and acquitted by a jury.
Are the suspects always identified?
No. The courts will usually impose an anonymity order banning the naming of the suspect to protect the individual. However, Mohammed Ahmed Mohamed can be named after the order was lifted to allow police to make a public appeal for information on his whereabouts.
When was the system introduced?
What did it replace?
The controversial control orders.
The measures, introduced in 2005, were much more restrictive - suspects could be relocated to a town far from their home, face 16-hour curfews and be banned from meeting named individuals and using mobile phones and the internet. As with TPims, they were ordered to wear electronic tags and report regularly to the police.
Critics considered control orders unfair and Kafkaesque.
Do TPims work?
Critics say they are too loose - "control orders-lite", as they were dubbed when they were introduced.
This latest disappearance is the second in less than two years. On Boxing Day 2012, Ibrahim Magag vanished after reportedly hiring a black cab. He has not been seen since.
Some also doubt the robustness of the electronic tags. Last week, prosecutions against three men, accused of tampering with their tags, were dropped when it emerged they might have inadvertently come loose.
There is also the wider question of how the police and MI5 will monitor suspects once the TPims expire after two years.
In the first official evaluation of the TPim, in March this year, David Anderson, a senior lawyer, said the government needed a higher standard of proof of threat before it applied to the courts for an order.
Mr Anderson, the government's independent reviewer of terror legislation, also said the Home Office needed to do more to develop what he called "exit strategies" for the terror suspects, to try to change their behaviour.