A public inquiry into the shooting of an unarmed man has found that Greater Manchester police (GMP) was entirely to blame for his death due to serious failings in its firearms unit.

Anthony Grainger, 36, was shot through the chest as he sat in a car in the village of Culcheth, Cheshire, by an armed police officer known as “Q9”. Detectives believed he and two others were planning to hold up a supermarket and had access to firearms on the evening of 3 March 2012. However, no weapons were found in the red Audi.

In a highly critical report on the incident published on Thursday, Judge Thomas Teague QC, concluded that GMP adopted a cavalier attitude and collated flawed intelligence during the botched operation directly leading to Grainger’s death.

Teague said the force’s armed response unit lacked the necessary degree of operational competence and following the shooting officers did not follow proper procedures, adopting a culture of “secrecy” and “arrogant disdain for the views of others”.

He added that the force repeatedly blocked the inquiry from obtaining relevant documents and evidence, with its tactical firearms unit (TFU) having an “unduly reticent” attitude and “general disinclination” to expose its decisions and actions to external scrutiny – a culture he believes persists to this day.

The commanders within the TFU were also repeatedly singled out for criticism for their gung-ho attitude towards firearms operations and their inability to explore safer tactical alternatives.

He added: “It is the senior commanders who set the tone of a specialised firearms department … the TFU remained incapable of exercising genuinely objective judgment in relation to its own conduct and that of its officers. They provide further evidence of an entrenched hostility to criticism.”

He made nine recommendations including a call for more openness and transparency following the discharge of a police firearm and for firearms officers to be equipped with body-worn video cameras as is now common practice for regular officers.

Outside the court Grainger’s mother, Marina Schofield, said she wanted officers to be held to account for her son’s death and confirmed that her legal team had contacted the Crown Prosecution Service (CPS) to examine whether criminal charges could follow against at least four senior police officers.

Leslie Thomas QC, representing the Grainger family, said he had been unlawfully killed by GMP due to a “calamitous combination of errors and blunders”.

He said the report catalogued “dishonesty and corruption” at the highest level of GMP and that senior officers had displayed a “cavalier approach to public safety”.

He added: “The chairman describes serious inaccuracies in threat assessments, seriously misleading briefings of firearms officers, a fundamentally flawed tactical approach, and planning of the operation that was incompetent and dangerous.

“Anthony died because of these failings by GMP.”

Meanwhile Grainger’s partner, Gail Hadfield-Grainger, said his death could have been prevented had it not been for a “litany of catastrophic failures” by GMP.

Hadfield-Grainger requested a meeting with the home secretary, Sajid Javid, describing her partner’s death as a national scandal.

She added: “He needs to explain to the public what he is going to do to make it safe for armed police to be deployed on the streets of Manchester.”

Father-of-two Grainger was behind the wheel of the stolen Audi when Q9 fired his MP5 submachine gun, striking Grainger fatally in the chest. Two other rounds were fired at the car’s tyres and a CS gas canister was thrown into the vehicle by another officer.

During 14 weeks of evidence in 2017, Q9 told Liverpool crown court from behind a screen that he believed Grainger had reached down as if to grab a firearm.

But the inquiry heard that no firearms were found on Grainger and he may have been reaching down for the driver’s door handle.

Describing the inquiry as “open and fearless” Teague concluded: “Q9’s mistaken belief that Mr Grainger was about to discharge a firearm was based on the inaccurate and inadequate briefing he had received that morning.

“That he jumped to the wrong conclusion is partly his own fault and partly the fault of his commanders whose incompetent planning and slipshod briefing directly contributed to his faulty appreciation of the facts.”

One of Grainger’s two passengers, David Totton, had been under surveillance for five months as part of Operation Shire, an investigation into their suspected involvement in commercial robberies.

However, Teague pointed out there was no intelligence to suggest on this occasion they were armed or had access to firearms.

He said: “At the root of the events of 3 March 2012 was a lack of effective leadership in firearms operations conducted by Greater Manchester police. I detected a deeply entrenched complacency among certain senior officers who lacked the necessary critical insight to detect, let alone remedy, the deficiencies I have identified.”

Since the shooting seven years ago there have been two inquiries into Grainger’s death. In 2013, an inquiry by the then Independent Police Complaints Commission concluded there had been 16 failings in the Grainger operation. They included that police marksmen had “conferred over witness statements”.

Steve Heywood, an assistant chief constable who retired from the force last year, faces a charge of gross misconduct. The inquiry heard that some of his notes had been written after the shooting, leading to a “false impression” of intelligence.

A spokesman for GMP said the force had made changes since the shooting and would now consider what more could be done.

GMP’s chief constable, Ian Hopkins, said in a statement: “Our failings have led to Anthony Grainger’s death and caused unimaginable harm to his family. For that I am sincerely sorry.”