New legislation designed to stop people with mental health problems being placed in custody for their own safety has been welcomed.
But there are warnings that it should not be seen as "an end in itself".
A joint review carried out by the Home Office and Department of Health states that children with mental health problems should never be taken to police cells, and that adults should not be taken to police stations except in "exceptional circumstances", which should be defined by law.
Chief Constable Simon Cole, national lead for mental ill health, said the proposals will help under 18s receive the right care at the right time.
"We have long said that police cells are never the right place for frightened and vulnerable young people," he said.
"However, this report is not an end in itself and important issues such as defining behaviour 'so extreme they cannot otherwise be safely managed' and the unique challenges presented by private homes will need to be addressed clearly going forward.
"Change on the ground will also be determined by the availability of local health-based places of safety."
The review on sections 135 and 136 of the Mental Health Act, announced by Home Secretary Theresa May at last year's Police Federation conference, set out a number of reforms to legislation in an attempt to reduce the number of people being taken to police cells as places of safety.
It found that one of the main reasons police cells were being used was because of a lack of health-based places of safety, something identified by Devon and Cornwall Assistant Chief Constable Paul Netherton last month.
A survey by the Care Quality Commission earlier this year found that the majority of local authorities are served by only one health-based place of safety, and 22 served by two. Many places can therefore only accommodate one person detained under s136 at a time.
Additionally, many providers operate policies which exclude young people and there are only four based places of safety in England specifically for young people. In 2013/14, 753 children and young people aged under 18 were detained under s136, 31 per cent of which were detained in police cells.
"I am very clear that this must not happen," said Ms May.
"It is vitally important for the person – someone who is experiencing a mental health crisis not suspected of any criminal offence – that they are dealt with by the right agencies. That means health services, not the police."
The review suggests amending the list of possible places of safety in s135 so that anywhere considered suitable and safe can be used as a place of safety - and found that on many occasions police officers have tried to use other places such as doctors surgeries but been refused.
Other suggested reforms include reducing the maximum length of detention in any place of safety from 72 hours to 24. It also suggests amending s136 - which currently deals with detaining a person in a public place - to include railway lines, private vehicles, hospital wards, rooftops of buildings and hotel rooms, in order to remove some confusion around the current law.
Doug Campbell, mental health lead for the Police Federation of England and Wales, said: "Anything which supports the safety of the public and doesn't end up unnecessarily criminalising people suffering from mental health problems is to be welcomed.
"It is imperative that people suffering these problems are dealt with in a health-based place of safety and not in a police cell. We would urge our health agency partners to ensure they have adequate resources in place to adequately handle these issues."
Shauneen Lambe, director of Just for Kids Law said the announcement was to be welcomed.
"We hope this heralds a whole new approach to the treatment of young people with mental health problems, which stops criminalising people for being ill," she said.