Health professionals have urged police to stop using the spray on psychiatric patients after a survey showed more than one-third of NHS mental health trusts had treated people sprayed by police.
But in a Lords written reply last night, Lord Williams of Mostyn said: "Regrettably, there may be occasions when police officers need to use force against people suffering from mental illness, and the use of CS spray may well represent the most benign option."
Researchers at the Bethlem and Maudsley Hospital NHS Trust said they were "appalled" last week to learn of 12 incidents in which the spray had been used to quell disruptive patients on hospital premises. Their report says the mentally ill are patients, not criminal, and urges action from the Department of Health.
Nineteen of the NHS trusts reported adverse effects of the spray on the health and safety of staff or patients; one nurse with asthma needed emergency treatment, and one trust reported seeing patients where CS spray had been regularly used once a fortnight. The "chemical strait-jacket" incapacitates victims, causing intense pain, especially around the eyes and can cause blistering and affect breathing.
Later effects include dermatitis and allergic sensitisation. High levels have also been linked to heart attacks. There are additional risks if the person affected suffers asthma or other breathing problems, is taking medication, and is also restrained. The hazards for those already on anti- psychotic medication are unknown.
Fraser Bell, a senior project nurse, said patients had to wait four hours for the spray's effects to wear off before nurses could touch them without becoming contaminated.
Mr Bell protested: "Rather than go through a long, involved process of negotiating and calming someone down they [the police] just reach for the spray, subdue them and nick them."
Defending the use of the spray, Lord Williams said its introduction had been welcomed, particularly by women police officers, because it was "seen as easy for even the slightest officer to use".
He added: "The effects of CS spray wear off relatively quickly and have no significant long-term effects. The physical impact involved in making a baton strike will inevitably carry a greater risk to the health of the person who is struck."
CS spray has been increasingly used by police to quell disturbances. In the past year it has been used against football fans, New Age travellers and protesting beef farmers. Since last October, it has been available to all members of the Metropolitan Police.
Five NHS trusts in the South and West, and four in the North-west had reported the use of CS spray by police.
One mental health practitioner told the researchers: "I thought CS [spray] was to help police prevent crime, not hit people with mental health problems. In the past, the police would have spent more time talking to patients. The spray seems like a short-cut, a quick and easy answer. These are patients that nurses deal with daily - we don't have to resort to this."