Police plans to withdraw from dealing with certain 999 calls have sparked "serious concerns" from mental health campaigners.
Norfolk Constabulary is set to adopt the controversial 'Right Person, Right Care' scheme which will see officers only respond to mental health-related calls if there is an immediate threat to life.
The force says this will free up officers to focus on investigating crime and that it will continue to attend when lives are in danger.
But mental health campaigners say they fear existing NHS services will not be able to cope without the same level of support from their police colleagues.
Mark Harrison, of the Campaign to Save Mental Health Services in Norfolk and Suffolk, said: "We completely understand why the police what to do this but we are very worried this will result in deterioration of services.
"From the experiences of people we have spoken to who have gone through mental distress, the police have dealt with them in very empathetic and sympathetic ways."
He added that without mental health services receiving an increase in funding it would be difficult to see the approach succeeding.
He said: "In our experience, the police are very good at de-escalation and if you do not have that as the first point of contact then you can end up in a situation where they would need to get involved anyway.
"Then you can find people needlessly ending up with criminal records because of their mental distress."
The campaign's concerns have been echoed by the Labour group at Norfolk County Council.
Its members have written an open letter expressing their fears to officials in the NHS, the police and the local care system.
The letter, which was written by deputy leader Emma Corlett, urges police to pause the plans.
It reads: "It is not acceptable that people in mental health crisis and their loved ones will get caught in the middle of a debate between different parts of public services about who should do what.
"It is not safe. It is not ethical.
"Locally the crisis pathway is fragmented, with people telling us they feel pushed from pillar to post with ever-moving goalposts about which service they can and should access and when.
"The social safety net is at its absolute weakest where it should be at its strongest."
Ms Corlett added: "There is a workforce crisis in mental health.
"Announcing this decision with an arbitrary timescale is not going to magic up additional qualified mental health staff in our crisis teams or accident and emergency.
"It is not going to magic up more local mental health beds or staff to care for patients.
"We urge you, as partners in the local system, to pause this and engage meaningfully with people who use services and community representatives."
It comes after the constabulary revealed plans to adopt the system which was pioneered by police in Humberside three years ago.
The Norfolk force aims to start working with the approach by the end of this year, to allow arrangements to be made with local health leaders and the mental health trust.
Simon Megicks, deputy chief constable in Norfolk, said: "We would never make a decision that would put people in danger, and we will continue to attend incidents where a crime has happened, or where there's harm or a risk to life.
"Policing will always have a role with people suffering mental ill-health, but we cannot bridge the gap in service provision of other agencies.
"This is not a sustainable position or one which is good for patients.
"Being dealt with by the police can have a detrimental impact on vulnerable people."
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