The government has secretly set up a VIP “stalker” squad to identify and detain terrorists and other individuals who pose a threat to prominent people.

The unit, staffed by police and psychiatrists, will have the power to detain suspects indefinitely using mental health laws.

The Fixated Threat Assessment Centre (FTAC) was quietly established last October and is set to reignite controversy over the detention of suspects without trial.

Until now it has been up to mental health professionals to determine if someone should be forcibly detained, but the new unit uses the police to identify suspects, increasing fears that distinctions are being blurred between criminal investigations and doctors’ clinical decisions.

The Metropolitan Police confirmed that the unit had been established only after its existence was revealed in a Sunday newspaper.

In a statement, it said: “The Fixated Threat Assessment Centre is a joint initiative between the Metropolitan Police, Home Office and Department of Health. Its role is to assess, manage and reduce potential risks and threats from fixated individuals, against people in public life, particularly protected VIPs.

“Fixated individuals are those who are abnormally preoccupied with certain ideas or people. Research has shown that a small minority exhibit violent behaviour.

“London-based FTAC is a pilot initiative, which was set up in October 2006 after research showed that no single unit existed to collate relevant information, assess the risks and initiate appropriate action to manage and reduce any threat.”

Staff at the central London centre will include four police officers, two civilian researchers, a forensic psychiatrist, a forensic psychologist and a forensic community mental health nurse.

It is being hailed as the first joint mental health-police unit in the UK and a “prototype for future joint services” in other areas.

The Mental Health Act requires two doctors or psychiatrists to approve a forcible detention, or “sectioning”, for treatment. It allows a patient to be held for up to six months before a further psychological assessment. Patients are then reviewed every year to determine if they can be released.

The government is trying to amend the act, with a controversial bill introduced in November, to bring in a wider definition of mental disorder in order to give doctors more power to detain people.

At least one terror suspect, allegedly linked to the 7/7 bomb plot and a suicide bombing in Israel, has already been held under the Mental Health Act. The man, who cannot be named for legal reasons, absconded from the hospital where he was being detained and has never been traced.

Liberty said the secret unit represented a new threat to civil liberties. Its policy director, Gareth Crossman, said: “There is a grave danger of this being used to deal with people where there is insufficient evidence for a criminal prosecution.

“This blurs the line between medical decisions and police actions. If you are going to allow doctors to take people’s liberty away, they have to be independent. That credibility is undermined when the doctors are part of the same team as the police.

“This raises serious concerns. First that you have a unit that allows police investigation to lead directly to people being sectioned without any kind of criminal proceedings. Secondly, it is being done under the umbrella of anti-terrorism at a time when the Government is looking at ways to detain terrorists without putting them on trial.”

FTAC was set up following an NHS research programme based at Chase Farm Hospital in Enfield, north London. Researchers examined thousands of cases of prominent people being stalked. It liaised with the FBI, the US Secret Service, the Capitol Hill Police, which protects Congressmen and Senators, and the Swedish and Norwegian secret services.

Sweden granted access to files on the murder of the foreign minister Anna Lindh who died after being stabbed by a stalker in a Stockholm store in 2003.

The research led to FTAC being set up with a £500,000-a-year budget from the Home Office and Department of Health.

Dr David James, FTAC’s senior forensic psychiatrist, has studied attacks on British and European politicians by people suffering pathological fixations. Also on the staff is Robert Halsey, a consultant forensic clinical psychologist who is a specialist in risk assessment.

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