New curbs to clamp down on the use of police custody to hold people in mental health crisis have taken effect.
Measures which came into force on Monday include a blanket ban on placing children in cells after they are detained under mental health laws.
For adults, the use of police cells as "places of safety" will only be allowed in exceptional circumstances.
The period for which a person can be detained for the purpose of a mental health assessment will also be cut from 72 to 24 hours.
The changes were announced by the Government last year following controversy over the detention in police cells of those who are not suspected of any crime.
Section 136 of the Mental Health Act 1983 sets out how police can remove to a safe place someone who appears to be suffering from mental disorder and in immediate need of care or control.
Figures show that in 2016/17, police stations were used following a section 136 detention on 1,029 occasions in England and Wales, including 20 where the detainee was under 18.
Both numbers have fallen sharply in recent years.
While 23 force areas reduced their use of police cells as places of safety for children to single figures or zero in the last year, the law change will ensure no child will end up in a police cell, according to the Home Office.
Minister for crime, safeguarding and vulnerability Victoria Atkins said: "Too often and for far too long vulnerable people experiencing mental health crisis, who have committed no crime, have found themselves in a police cell because there is nowhere else to go.
"This Government has been clear that the best place for people suffering mental health crisis is a healthcare setting and not a police station.
"The change in legislation will build on progress already made by police forces and health care partners that saw use of police cells for those experiencing a mental health crisis halve in the last year."
Health minister Jackie Doyle-Price said: "When you are experiencing a mental health crisis, the last place you'd want to be is in police custody and it is totally inappropriate for a child to be taken to a cell just because they are ill.
"We have seen a 90% reduction in England in the number of people being held in custody who should be in NHS care - this move will mean that for young people this will finally be a thing of the past.
"We are also investing £30m to increase and improve places of safety for people in crisis."
The changes come days after police chiefs warned thousands of people could be being held unlawfully because of difficulties accessing hospital beds.
Senior officers raised the alarm after a review found individuals have been kept beyond the maximum custody period for their own safety.
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