The Metropolitan police has won its battle to stop attending most of the mental health calls it receives after a tense behind-the-scenes row with the health service, the Guardian has learned. From 31 October the Met will start implementing a scheme that aims to stop officers being diverted from crime fighting to do work health staff are better trained for. In May, the Guardian revealed that the Met commissioner, Sir Mark Rowley, had written to health and social care leaders setting a deadline of 31 August – leading to furious reaction from health chiefs who wrote to the commissioner protesting that it would put vulnerable people at risk. The agreement means Rowley will push his deadline for the start of the changes back by two months, before a phased introduction. Health services will not publicly criticise the police decision, and will race to put measures in place to pick up the work. A formal announcement is expected as soon as Friday 18 August after weeks of tense talks. The Met was armed with legal advice from a senior barrister – a king’s counsel – arguing the law meant the force did not have to do the work of the health service and would probably win any legal challenge. Police will continue to attend calls if there is a risk to life, a danger to the public or a crime is believed to be taking place. The agreement says: “The threshold for a police response to a mental health-related incident will be to investigate a crime that has occurred or is occurring; or to protect people, when there is a real and immediate risk to the life of a person, or of a person being subject to or at risk of serious harm. “The need for this threshold to change is seen through our data. For example, we know that 78% of people detained under section 136 will go on to be discharged home following assessment, suggesting mental health is being over-policed in London.” One health source with knowledge of the discussions told the Guardian the commissioner’s hard line was disliked, but had worked: “He got us round the table, got our attention and got us talking. “It’s not malice but the NHS is notoriously slow. If he [Rowley] did not give a deadline, we would have been here for 10 years.” The scheme is called Right Care Right Person (RCRP), and has been agreed nationally by government departments and national police and health bodies. Actually implementing it is down to local areas. NHS London has already started sending guidance to staff about what the new scheme may mean. The letter sent on Thursday says: “In practice, this means that police call handlers will receive a new prompt relating to welfare checks or when a patient goes absent from health partner inpatient care. The prompt will ask call handlers to check that a police response is required or whether the person’s needs may be better met by a health or care professional.” Among police forces, the Met is thought to be an outlier, in effectively making a threat and giving an ultimatum, police and health sources say. Rowley’s letter in May summoned health and social care chiefs to meetings, which were held at the Met’s Scotland Yard central London headquarters and NHS offices in Waterloo. One health source with close knowledge of the negotiations said: “There is nothing in their presentation you could disagree with. “There has been a kneejerk reaction from health and social care, to call the police.” RCRP was pioneered by Humberside police, who believe it freed up 7% of officer time to do what the police are legally responsible for. Health chiefs in London say they do not know how they will meet the new demand. A source said: “The health service is already overloaded, the winter crisis is coming, and London ambulance service already faces big performance pressure.” One reason for the Met to delay, other than giving the health sector more time to prepare, is so that police call centres are better prepared to deal with the new system, a police source said. The RCRP scheme has four stages. The first the Met is expected to implement arecalls to check on welfare, for instance where a mental health patient has missed an appointment and where there is no intelligence of harm. The second stage is when a patient leaves a health facility, having been there voluntarily. The third is handing over patients to the health sector, where officers can endure long waits of up to 14 hours, and the fourth stage is transporting people to a mental health facility.