In law, police have no special protection if they shoot a suspect dead in the course of their duties. They do so lawfully if they hold an honest belief that a suspect threatens the life of themselves and others. In practice, prosecutors have been wary of bringing charges and juries have been reluctant to pass guilty verdicts. No police officer has ever been convicted of breaking the law by shooting a suspect dead.

This year a former Met police firearms officer, Anthony Long, was cleared of murdering a suspect, 10 years after the shooting. Azelle Rodney was shot on sight by Long – including four bullets to the head – in 2005 in north London. Long argued self-defence, which the jury accepted, after he told them he feared the suspect was reaching for a gun.

By law police shootings must be investigated by the IPCC. Officers delay investigations by refusing to answer oral questions in interview, the IPCC has said.

Firearms officers in the Met are a powerful and close-knit group. They are volunteers and have expressed their anger in the past by threatening to hand in their weapons. Such a prospect catches the attention of their bosses and politicians, especially amid heightened fears of a terrorist gun attack in the UK.

In a candid 2014 Guardian interview, commander Neil Basu, then a Met firearms boss, explained the feelings of armed officers. He said: “No amount of fantastic Churchillian leadership from me is going to make an officer want to contribute to an inquiry where they are being made a suspect. They will be legally advised to make no comment. Why wouldn’t they, knowing that the slightest mistake they make … and they are potentially facing a murder charge for doing their job?”