Far more can be done to save lives say campaigners after the first survey of its kind found that nearly 600 prisoners die in custody each year.
Most of the deaths involved people with mental illness and a significant proportion were self inflicted, the survey found, leading to claims that overcrowding and underfunding were contributing factors.
The study brings together for the first time records of people who died while being held in prisons, police cells, and other places of detention such as immigration centres and secure hospitals. The total was 586 in 2005-06 and 590 in 2004-05. Some 351 died while being detained under the Mental Health Act last year, although most of those died of natural causes. But 68 of the 156 men who died in prison killed themselves.
Overcrowding in prisons in England and Wales has coincided with an increase in the number of self-inflicted deaths this year. There have been 68 cases so far in 2007 compared with 46 at this point last year.
The figures were produced by the Forum for Preventing Deaths in Custody, which brought together groups including the National Offender Management Service, the Association of Chief Police Officers and the Independent Police Complaints Authority. John Wadham, the chairman of the group, said: "Six hundred deaths is a very significant figure.
"The number of deaths in custody is the mark of a civilised society. I think this is too high and we need to reduce it. We have found weaknesses in some of the systems and we know that more could be don."
Nick Herbert, the Shadow Justice Secretary, said: "The Government's own figures show that suicides are far more likely in overcrowded jails and that an inadequate number of new prison places will not keep pace with the rising custodial population."
Maria Eagle, the Justice Minister, welcomed the report. She said: "There are clearly lessons arising from many of the deaths in custody each year and the Forum plays an important part in helping organisations to learn from these."
Jack Straw, the Secretary of State for Justice, told GMTV: "We're very concerned indeed, particularly about avoidable deaths in custody. Two thirds of the deaths that occur in custody occur by natural causes. I'm terribly sad when anybody dies, but that's just the fact of life.
"On the avoidable deaths that include obviously self-inflicted deaths, suicides, we're working very hard; we have done over many years, to get that number down."Reuse content