The family of PC Keith Palmer, murdered during a terrorist rampage on parliament, accused senior Metropolitan police officers of “closing ranks” after a coroner ruled on Wednesday that his death may have been prevented had armed officers been closer.

The ruling highlighting “shortcomings” in how armed officers were managed by their bosses was a victory for Palmer’s family, angered by details that emerged during the month-long inquest of how the officer had been left vulnerable.

After the verdict, the Met dropped its claim that Palmer’s life could not have been saved had armed officers been nearer to him when the attack happened.

A Met chief stayed in his car during an attack. That’s not leadership | Gaby Hinsliff Read more

Palmer’s widow, Michelle, who has been left to raise their daughter, Amy, alone, said: “How could Keith have been left alone, unarmed, guarding an open gate at one of the most iconic buildings in the world and one of the country’s top terrorist targets? He was left at a vulnerable location, with no protection, to die. The fact there were no firearms officers there for nearly an hour is hard to believe.

“I truly believe that if they had been there he would still be here today and Amy wouldn’t have lost her daddy.”

Palmer’s parents and siblings said: “We expected the Met to welcome an open and transparent examination of this horrific attack on its own officer and members of the public, yet instead senior officers seem to have closed ranks.”

Palmer, who was unarmed, was fatally stabbed last March as he guarded Carriage Gates at the Palace of Westminster in an attack carried out by Khalid Masood.

Palmer, 48, was one of five people killed during the attack that lasted 82 seconds on 22 March 2017.

It started with Masood, 52, turning a vehicle into a weapon to plough into pedestrians on Westminster Bridge. He killed Kurt Cochran, 54, Leslie Rhodes, 75, Aysha Frade, 44, and Andreea Cristea, 31, before crashing into a barrier at the Palace of Westminster. Amid the chaos, he jumped out of the vehicle, and ran towards the gates of parliament, where he repeatedly slashed at Palmer and fatally wounded him.

Masood’s attack was halted when he was shot dead by an armed officer guarding then defence secretary Michael Fallon.

The inquest had heard armed officers had not been near the gates in the hour before the attack, and believed their orders were to patrol the grounds, when in fact they were to stay near the gates.

The conclusion from the chief coroner, Mark Lucraft QC, attributed blame to errors by the Met. In his ruling, he said: “Due to shortcomings in the security system at New Palace Yard, including the supervision of those engaged in such duties, the armed officers were not aware of a requirement to remain in close proximity to the gates.

“Had they been stationed there it is possible that they may have been able to prevent PC Palmer suffering fatal injuries.”

The anger Palmer’s family felt towards the Met had grown throughout the inquest. The finding by the coroner was greeted by statements stinging in their criticism, made all the more serious for the Met’s leaders because they are the grieving loved ones of an officer viewed by the rank and file as a hero who paid the ultimate sacrifice doing his duty.

Lucraft said Palmer had acted heroically when he confronted Masood during the attack. “It was an extremely brave thing for him to do. It was clear that he was fulfilling his job of protecting the palace and those within it,” he said.

Khalid Masood: from Kent schoolboy to Westminster attacker Read more

Two armed officers, PC Lee Ashby and PC Nicholas Sanders, were on duty in New Palace Yard at the time of the attack. The inquest previously heard that the two officers had unknowingly disobeyed instructions, which required roving firearms officers to be in close proximity to the gates but not outside them, and not to work in pairs. Instead, the officers were near the members’ entrance to parliament. CCTV footage showed that the last time armed officers were at the gates was at about 1.45pm, almost an hour before Palmer was attacked at 2.41pm.

Assistant commissioner Neil Basu, Britain’s most senior counter terrorism officer, said: “The chief coroner has plainly carried out a rigorous and full enquiry and we unreservedly accept his conclusions.

“Even the possibility that the MPS lost the chance to prevent the murder of a brave and courageous officer is unacceptable. For the loss of that possibility to protect him from Khalid Masood, we are deeply sorry.

“Security arrangements have been substantially changed since the terrible events of 22 March 2017. However, everything that we can possibly do to improve the position further, and we await the chief coroner’s detailed conclusions, will be done.”

Basu said Palmer had “acted with tremendous bravery and heroism” during the attack, and added that “his courage will never be forgotten”.

Earlier, Hugo Keith QC, representing the Met police, argued against claims by Palmer’s family that having armed officers at the carriage gates could have saved his life. He said that even if the armed officers had been at the gates, there was little evidence they would have been in the position to “neutralise” Masood. He described suggestions they would have been able to take a shot as “entirely speculative”.

Palmer’s widow, Michelle, criticised the Met’s approach to the investigation: “What is so disappointing is that the police haven’t been very open about their investigation in relation to the security arrangements at the Palace of Westminster. They have been very slow to get to the bottom of how this was allowed to happen.

“Nobody wants to take responsibility for leaving one of their own officers there unprotected when they knew that police officers were at risk of attack at this vulnerable location.

“What makes it even worse is that this lax security had been carrying on for years and it has taken what happened to Keith for things to change.”

During his conclusion, which lasted more than three hours, Lucraft summarised the main evidence of the inquest and expressed his condolences to the families and praised them for the “great dignity” they had shown throughout the proceedings. He thanked emergency personnel who rushed to assist the injured, as well as the members of public who helped.

But he said some members of the public chose to photograph and film the aftermath of the attack rather than respond. “Sadly, some people, for whatever reasons, have posted some material on the internet,” Lucraft said. He called for the material to be removed as it was “distressful” to the families.

All five victims who died in the attack were unlawfully killed, Lucraft also ruled.

Lucraft gave his verdict after a month-long inquest into the attack. He added that article 2 of the European convention on human rights – protecting the right to life – was engaged in relation to Palmer’s death. He said he would provide full reasons for that decision in due course.

Article 2 can be engaged if there is evidence to suggest that systemic failures contributed to an individual’s death. It could lead to a broader inquiry into the death that considers state and statutory negligence.