Commissioner Sir Mark Rowley has told health and social care services that officers won't be sent unless there's a threat to life.

It's intended to allow police to focus on crime and its victims rather than dealing with people who need expert medical help.

"Where there is an immediate threat to life, officers will continue to respond," the Met Police said.

"In the interests of patients and the public, we urgently need to redress the imbalance of responsibility, where police officers are left delivering health responsibilities.

"Health services must take primacy for caring for the mentally ill, allowing officers to focus on their core responsibilities to prevent and detect crime, and keep communities safe and support victims."

Former Her Majesty's Inspector of Constabulary Zoe Billingham told Sky News she had reservations over the move, saying: "I do find this really rather concerning.

"The police are the only people with the powers to be able to make that immediate as soon as the police have attended, and some forces are sending police officers with mental health professionals and nurses and so on."

She added: "Resorting to brinkmanship and ultimatums - that's now always the right way forward."

Ms Billingham also said that there needs to be millions in investments to improve mental health services in the NHS.

A Met spokesperson told the BBC that officers spent an average of 10 hours with a patient when they are sectioned under the Mental Health Act.

"In London alone, between 500-600 times a month, officers are waiting for this length of time to hand over to patients, and it cannot continue," said a statement.

"Police... are not trained to deliver mental health care."

Humberside brought in a similar policy - known as Right Care, Right Person (RCRP) - in 2020 that involves staff from the charity Mind dealing with calls in the police control room.

It saved 1,100 police hours per month and people received "more timely care from the most appropriate care provider", according to a November report by His Majesty's Inspectorate of Constabulary, Fire and Rescue Services.

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'We are failing patients'

RCRP is designed to be implemented nationally, but the Met commissioner is believed to have lost patience.

In his letter to health and social care services, first reported by The Guardian, he writes: "I have asked my team that the Met introduce RCRP this summer and withdraw from health-related calls by no later than August 31.

"It is important to stress the urgency of implementing RCRP in London.

"Every day that we permit the status quo to remain, we are collectively failing patients and are not setting up officers to succeed."

He continued: "We are failing Londoners twice.

"We are failing them first by sending police officers, not medical professionals, to those in mental health crisis, and expecting them to do their best in circumstances where they are not the right people to be dealing with the patient.

"We are failing Londoners a second time by taking large amounts of officer time away from preventing and solving crime, as well as dealing properly with victims, in order to fill gaps for others.

"The extent to which we are collectively failing Londoners and inappropriately placing demand on policing is very stark."

He added the Met had received a record number of 999 calls on 28-29 April but only 30% were "crime related".

Dal Babu, a former chief superintendent in the Met, told Sky News that it is "very dangerous to be alarmist about this" change.

"I think what the police are clearly very, very frustrated with, is the fact that they are taking on more and more responsibilities for dealing with people who are in mental health crises."

Mr Babu added: "Over the years more and more demand is being made of the police and I think this is a conversation around how do you ensure that everybody is resourced appropriately and there is a proper handover from one agency to another agency."

He also described the training of officers for mental health situations as "not particularly significant given how many calls the police have to deal with".