The Metropolitan police has called on the SAS to provide counter-terrorism support after firearms officers downed their weapons in protest at the charging of their colleague with murder. Suella Braverman ordered a review of armed policing to calm a growing rebellion of about 100 officers over the charging on Wednesday of an officer for the murder of 24-year-old Chris Kaba, an unarmed man killed last September by a single shot to the head. Met commissioner Sir Mark Rowley called for greater protections for armed officers, accusing the police watchdog of being too quick to criminally investigate those who use force. The scale and speed of the protest by Met armed officers prompted the home secretary to order an emergency review of armed policing, with several sources telling the Guardian there were fears the rebellion could spread further within the Met and around the country. The Met, which polices most of London, had to ask other smaller forces to lend it armed officers and then on Sunday to ask the military for help. The Guardian understands that the Met asked for soldiers from the SAS to be put on standby for deployment against terrorist suspects, as a significant number of police counter-terrorism firearms officers refused to be available for armed duties. It is understood the soldiers would be used if police counter-terrorism commanders believed they needed to stage a raid. The military personnel would not be deployed on armed patrols on the streets of London. A Met police spokesperson said: “The Ministry of Defence has agreed to a request to provide the Met with counter-terrorism support should it be needed.” A Ministry of Defence spokesperson said: “We have accepted a military aid to the civil authorities request from the Home Office to provide routine counter-terrorism contingency support to the Metropolitan police, should it be needed.” Ordering the review of armed policing on Sunday, Braverman said: “We depend on our brave firearms officers to protect us from the most dangerous and violent in society. In the interest of public safety they have to make split-second decisions under extraordinary pressures. “They mustn’t fear ending up in the dock for carrying out their duties. Officers risking their lives to keep us safe have my full backing and I will do everything in my power to support them. That’s why I have launched a review to ensure they have the confidence to do their jobs while protecting us all.” But her intervention has been criticised by opposition politicians, legal figures and civil rights campaigners. Labour’s Harriet Harman said: “Nothing must be done or said by any of us which would tend to interfere with the criminal justice system in any case.” Tight rules govern reporting of criminal trials to ensure they are fair and nothing prejudices them. The trial of the police officer – known only as NX121 – is not scheduled until next year. Deborah Coles, the executive director of Inquest, said: “The suggestion that there is something in the law or legal process that is biased against serving police officers does not bear scrutiny. Police firearms officers must remain accountable to the rule of law.” Rowley released a letter on Sunday night arguing that the rules around police use of force needed reform. He said the government-ordered review should investigate how the Independent Office for Police Conduct pursued officers and how the Crown Prosecution Service considered criminal charges against them. He said of 4,000 armed incident a year on average, Met officers opened fire only twice on average. The commissioner said the system for investigating officers was too slow and “ties itself in knots” convicting bad officers but was too quick to accuse good officers who faced years of uncertainty. The IOPC’s threshold for investigating an officer should be raised, the commissioner said, and the review should examine how the CPS can give greater protection for officers who use force. Rowley’s aides are aware that with his comments the commissioner risks further alienating sections of the public who believe police are not accountable enough. So far, face-to-face attempts by Rowley and a top aide to placate firearms officers have been rebuffed, with sources saying there was “tough talking” on both sides. The Guardian understands that the Police Federation has had legal advice that firearms officers can be ordered to carry out their duties if they threaten to down their weapon without due notice. Since the announcement of the murder charge on Wednesday, some have told their commanders they needed a period to reflect on whether they wish to continue carrying a gun. Some are talking to their families about whether the risks are worth it. Spreading disaffection in the ranks is an offence punishable by imprisonment or fines under the 1996 Police Act. The Met’s armed policing command was lambasted by the Casey review published earlier this year into the Met as riddled with bias, and with some claiming unwarranted expenses and perks.