A man was shot dead by a police firearms officer despite "complying" with instructions to put his hands up, legal documents claim.
Jermaine Baker died after armed police foiled an attempt to free a prisoner near Wood Green Crown Court in 2015.
Papers submitted to the Court of Appeal on behalf of the Independent Office for Police Conduct (IOPC) say the officer thought Mr Baker was getting a gun.
But the IOPC says it was a "mistaken and unreasonable" belief.
The watchdog is challenging a court ruling blocking them from bringing misconduct proceedings against the officer, known as W80, for the use of "excessive" force.
Mr Baker was in the front passenger seat of a stolen Audi, along with two other men, waiting for Izzet Eren to arrive in a security van from Wormwood Scrubs prison to be sentenced for a firearms offence, in December 2015.
While monitoring the three men via two bugging devices police moved in on the vehicle and 28-year-old Mr Baker was fatally shot by W80.
According to a submission from Tim Owen QC, who is representing the IOPC, W80 maintains that Mr Baker moved his hands "up towards a bag slung around his shoulder... despite calls to put his hands on the dashboard".
"W80 says that this action caused him honestly to believe that Mr Baker was reaching for a firearm and put him in fear of his life and that of his colleagues," the document says.
"However, the evidence shows that there was in fact no gun in the bag and that the instructions given immediately prior to the fatal shot were for Mr Baker to put his hands up," Mr Owen's submission continues.
"The evidence also shows that the position of Mr Baker's hand at the time he was shot was consistent with him putting his hands up in compliance with one of the instructions given to him."
Lawyers for W80, who are opposing the IOPC appeal, say police had been provided with intelligence that those involved in the plot had firearms - a replica Uzi machine gun was found on the floor of the car next to a back seat.
In 2019, the High Court ruled that an attempt by the IOPC to launch disciplinary proceedings against him for gross misconduct was unlawful because the watchdog had applied the wrong legal test in assessing the officer's claim that he had acted in self-defence.
The court said the IOPC should have applied the criminal law test, meaning W80's belief that his life was in danger when he opened fire would not have to be judged on whether it was "reasonable".
At the start of a three-day appeal, Mr Owen said the High Court ruling was "wrong".
His legal submission says that if the judgment is allowed to stand, "firearms officers who make honest but unreasonable mistakes when using potentially lethal force cannot face any disciplinary proceedings for their conduct".
In legal documents presented to the appeal judges, Rosemary Davidson, who is representing W80, says he has a "legitimate expectation" that the criminal test for self-defence will be applied.
"It would be an abuse of power for the [IOPC] to adopt a different test at this late stage in the disciplinary process," she says.