More than 100,000 beat officers have been issued with canisters of CS and, according to figures obtained by the Independent on Sunday, its use has become commonplace - despite serious questions about health risks.
Civil liberties groups and health experts have pointed to dozens of cases in which CS spray has been used in situations where the threat to officers' safety has been negligible or non-existent. Of particular concern is the way in which it has been used to restrain the mentally ill.
Last week the Independent on Sunday revealed for the first time that police across Britain are regularly using CS spray as a "chemical straitjacket" to subdue mental patients. Now a 28-year-old mentally ill man is suing police for alleged assault with CS spray and for violating his rights as a patient. In the first case of its kind in the UK, lawyers acting for the man are suing for assault and for exemplary damages for police violation of his constitutional rights as a patient being detained under the Mental Health Act.
The use of the CS spray is now so prevalent that when Thames Valley Police began trials last week, it became the 40th force to do so. Only Nottinghamshire, Northamptonshire and Sussex constabularies have resisted the pressure to issue CS sprays.
Evidence that CS spray is quickly replacing the baton as the weapon of choice among officers emerged in a report by West Midlands police, published last week, which revealed that between July and September last year, the spray was used 203 times. During the same period, the baton was used at 82 incidents.
The Police Complaints Authority (PCA) has received 254 complaints from the public about CS spray. John Cartwright, the PCA deputy chairman, said: "I am concerned that it is sometimes being used as a convenience and inappropriately. Some officers are tempted to use it too soon."
The Association of Chief Police Officers (Acpo) has championed the use of CS spray as a potential police life-saver, claiming it is a vital weapon in redressing the balance in the fight against violent criminals.
Both Mind, the mental health charity, and the civil rights group Liberty want CS spray to be banned. A spokeswoman for Liberty, Liz Parratt, said: "It is part of the drift to policing by coercion and a move away from policing by consent. It raises serious civil liberties issues."
Ms Parratt said police often ignored Acpo's guidelines and used the spray indiscriminately. She cited one occasion when CS was allegedly sprayed into a crowded coach and the doors slammed shut, and another where CS spray was said to have been used during an incident in a children's home. Other examples include the spraying of an elderly Alzheimer's patient and a pregnant woman.
The threat to the health of those exposed to CS spray remains an area of deep concern, said Ms Parratt. "More research needs to be done," she said.
Special report, page 6