Jonathon Zito was murdered in a headline-grabbing case

The study said the Zito Trust had, despite its sensitivities, probably only served to highlight the rare killings by mentally ill people.

The trust was founded in 1994 after a schizophrenic patient killed Jonathon Zito on a London Underground station platform in 1992.

The study said heightened awareness of such crimes had led to "a sense of needing some sort of action" on care in the community.

Whatever reasons for reviewing the scheme are necessary, "presumed homicidal tendencies of people with a mental disorder need not be among them", it said.

However, Michael Howlett, director of the Zito Trust, said: "The view that highlighting the need for reforms increases the stigmatisation of the mentally ill is not supported by the evidence."

He also questioned whether it was possible to say that the number of murders committed by mentally ill patients was going down.

He said: "We have already shown in research not cited by Professors Taylor and Gunn that it is extremely difficult to determine trends, given the way the statistics are collated."

Perspective

The study drew attention to other risks in the community.

It said 600 to 700 incidents a year were recorded by the police as homicide, 300 deaths resulted from "dangerous, drunken or drugged driving or aggravated vehicle taking".

There were also 3500 to 4000 deaths a year from road accidents.

The authors said they had found no evidence to suggest that there was an increase in the number if strangers killed by mentally ill people.

Professor Taylor said: "It is important that people put this into some sort of perspective. Every week someone in the UK wins the jackpot on the National Lottery, but 54,999,999 don't.

"The odds are probably even more against a person losing their life to someone with mental illness. When it happens, a mother, father, sibling, spouse, child or other close contact is more likely to be the tragic victim."

But Mr Howlett said that such comparisons with the National Lottery and drunk driving were "meaningless" and "insensitive".

Marjorie Wallace: "Flaws and faultlines of the system"

The mental health charity SANE has investigated the summaries and recommendations of 23 homicide inquiries involving mentally ill people in which 35 lives were lost.

One in three of the homicides were judged to be either predictable or preventable.

Marjorie Wallace, chief executive of SANE, said: "The success or failure of community care should not be measured by statistics such as the overall number of homicides - or suicides - committed by mentally ill people.

"It benefits no-one to ignore the flaws and faultlines of a system whose failings are exposed time and again when a tragedy is investigated.

"Only by confronting the failures of the policy can we prevent future headline cases which damage the majority of mentally ill people who are never violent."