Police chiefs have formally asked the government to make it harder to investigate and prosecute officers after the fatal shooting of Chris Kaba led to a Scotland Yard sergeant being acquitted of murder, the Guardian has learned. Campaigners have criticised the move, saying calls to redraw the rules were a cynical attempt by police leaders to secure “effective immunity” for their officers. The home secretary is expected to make an announcement imminently about speeding up a review of how police are held to account in England and Wales. A jury took three hours on Monday to throw out the murder charge against Sgt Martyn Blake, the Met police officer who shot dead Kaba, an unarmed suspect. Demands for change have been lodged with the government by the National Police Chiefs’ Council, including a call to make it harder to find officers guilty of unlawful killing at inquests, and also the right for the accused to remain anonymous until conviction, if charged with an offence committed while exercising their duties. The changes would cover all use of force while on duty, not just shootings, while also offering “greater protections” for police drivers who injure members of the public, or crash. As well as the NPCC, the Metropolitan police have also called for change. The force has asked for anonymity for firearms officers as a minimum, and for all officers who face criminal charges resulting from their duties, until a jury returns a guilty verdict. The officer in the Kaba case, Blake, was named six months after being charged with murder, after a legal challenge to his anonymity by British news organisations. Among the measures police chiefs who make up the NPCC have presented to the government are: Making it harder for the Crown Prosecution Service to charge officers, with police chiefs proposing prosecutors would have to prove training or approved professional practice was not being followed before taking action. Changing the standard of proof required for a verdict of unlawful killing before the inquest into Kaba expected as early as next year. Currently the ruling is made on a balance of probabilities, the civil standard. Police chiefs want it to be the criminal standard, which is beyond reasonable doubt. Making it harder to disprove a claim of self-defence in misconduct inquiries, by changing the standard to the higher criminal test, rather than the current civil test. The head of the leading group for state accountability after deaths condemned the demands. Deborah Coles, the director of Inquest, which supported the Kaba family, said: “The cynical attempts to protect the police from the rule of law must be rigorously resisted, as this is in effect giving them immunity. “Given the disquiet about police killings, the use of force and cultures of racism and misogyny within the police, this will be seen as calculated attempts to evade scrutiny and accountability and further erode public confidence.” A police source with knowledge of discussions denied the move was about securing immunity for officers. The government faces a balancing act in the coming weeks of ensuring officers have the confidence to use their powers while also reassuring communities that police are not above the law. The requests from the Met commissioner, Mark Rowley, would make it less likely officers would face disciplinary or criminal sanction over allegations directly resulting from their exercise of police powers while on duty. A source said with knowledge of Rowley’s thinking said: “The CPS would have to explain how an officer had departed from their training or policy, as an additional threshold before bringing charges. “There may be learning, but is a punitive measure appropriate in the majority of cases? There will always be exceptions.” The source stressed the Met did not support greater protection for officers facing allegations while off duty. It means Wayne Couzens, who while a Met officer kidnapped and murdered Sarah Everard, and officers unmasked as serial sex offenders would continue to be pursued and named on charge. The commissioner has warned that fear of investigation and the length of time it takes has led to less stop and search and fewer officers willing to carry a Taser, while the confidence of his firearms officers has been rocked by the charging of Blake. Multiple sources said these concerns were most acute in the Met, where it was feared a guilty verdict against Blake would have led to a large walkout by its firearms officers – though a significant protest was not expected in other forces around England and Wales. Blake was the second Met firearms officer charged, tried and acquitted of murder, the last being Anthony Long in 2015 after the killing of Azelle Rodney a decade earlier. The family solicitor in both cases was Daniel Machover, who said many of the rules police wanted weakened came from supreme court rulings: “These proposed changes are both alarming and wholly inappropriate in a modern democracy. What we need as a society is better accountability and not more hurdles to accountability.” Some in the Met believe officers face a politically driven witch-hunt. Long said: “The IOPC [Independent Office for Police Conduct] are not very talented investigators and they are desperate to prove their credibility to the black community.” The Met has been monitoring community reaction especially in black communities, and has so far detected less anger than feared over Blake’s acquittal. The firearms officer shot the unarmed Kaba in the head when the car was forced to stop, after the vehicle was linked to a firearms incident. Blake told the jury he feared an officer could have been run over in Kaba’s effort to escape. On Tuesday legal restrictions were lifted allowing it to be reported that Kaba was pictured on CCTV shooting a man on a nightclub dancefloor days before he was shot by police, and was alleged to be a core member of the south London-based 67 gang. Details of Kaba’s past offending were not put before the jury in the murder trial at the Old Bailey because the judge, Mr Justice Goss, ruled they were not relevant. Blake, at the point he pulled the trigger on 5 September 2022, did not know these details nor who was in the car.