- Video report by ITV News Correspondent Sejal Karia
The widow of Pc Keith Palmer says her husband was left in a "vulnerable location with no protection to die".
Pc Palmer was stabbed to death at the gates to the Palace of Westminster when he confronted Khalid Masood on 22 March 2017.
A coroner concluded that is "possible" that Pc Palmer's death could have been avoided if armed police officers were stationed at the Carriage Gates at the Palace of Westminster when Masood attacked.
Chief coroner Mark Lucraft QC said "shortcomings in the security system" at New Palace Yard, including the supervision of armed officers, meant they were unaware they should have been on guard near the gates at the time of Pc Palmer's murder.
Michelle Palmer, Pc Palmer's wife, said in a statement: “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," Mrs Palmer added. "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."
Mrs Palmer criticised how long it had taken for the authorities to get o the bottom of what happened on that day.
"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."
Mrs Palmer says she was pleased that the coroner found shortcomings in the security system relating to the senior command of the Metropolitan Police but it won’t bring Keith back.
"They let Keith down by failing to protect him and let us down by failing to investigate his death properly. Now we have to live with the consequences of their failure.”
Patrick Maguire, Mrs Palmer's lawyer, added: "While we welcome the coroner’s findings that there were shortcomings in the security system by the senior command of the Metropolitan Police we still feel there are many unanswered questions about how this was allowed to happen. We have concerns that the full facts will never come out.”
Masood had already fatally injured four people on Westminster Bridge after deliberately driving a car into them by the time he reached the Carriage Gates. The five victims of the Westminster attack: Andreea Cristea, Kurt Cochran, Aysha Frade, Leslie Rhodes
After crashing his car, Masood ran to the gates, where he stabbed Pc Palmer 12 times, before entering the grounds when he was shot three times by a plainclothes police officer.
Coroner Lucraft QC has concluded that all five victims of the Westminster terror attack, the other four being Andreea Cristea, Kurt Cochran, Aysha Frade and Leslie Rhodes, were "unlawfully killed".
Mick Mountain performed the same role as PC Palmer for 18 years from 1995 until he retired in 2013, having been the oldest and longest serving officer in the Metropolitan Police.
Asked if the Metropolitan Police failed PC Palmer, Mountain told ITV News: "Yes, they did because they didn't give him and all the officers who worked those gates and other places, there are other gates around as well, they didn't give them the protection that was required in this day and age, the way things have changed in the world.
"And everybody knew the way the world had gone and all these different attacks at different places and they most certainly needed more protection than was given to us.
A key problem for Mountain was a change in policy regarding the posting of armed officers at the gates. They were mandatory prior to 2012 but then the rules changed, leaving Mountain feeling vulnerable when protecting Parliament.
He had previously voiced concerns about the policy change but says he was ignored by his superiors.
"They failed us, they should have had them there and they should have done something to the comments made to them.
"They ignored our concerns, devastating for the police officer, Keith, who died. He did his job the best he could and, obviously, suffered the consequences of what? Being a police officer in a situation of the world as it is today."
Assistant Commissioner Specialist Operations, Neil Basu, says that it is "unacceptable" that the police even potentially missed the opportunity to avoid Pc Palmer's death.
Asst Commissioner Basu said: "On the 22nd March last year five people lost their lives during an horrific act of terrorism in Westminster with devastating consequences for their families, friends and all those who tried to help them.
"We unreservedly accept his conclusions.Even the possibility that the Met lost the possibility of saving such a brave and courageous officer is unacceptable. For that loss of possibility to protect him from Khalid Masood, we are deeply sorry.
"Security arrangement have been substantially changed since the terrible events of 22nd March 2017. However, everything that we can possibly do to improve the position further, and we will await the coroner's detailed conclusions, will be done.
"What is also clear is that Pc Palmer acted with tremendous heroism and bravery in confronting Masood at the gates of Parliament in carrying out his duties as a police officer. His courage will never be forgotten."
Ken Marsh, chairman of the Metropolitan Police Federation, said: "March 22 2017 is day we all shall never forget. In under 90 seconds a terrorist attacked the heart of our democracy, sadly killing members of the public and murdering a brave police officer.
"The thoughts of all officers in London remain with hero Pc Keith Palmer, his family, and all those affected by the attack. Including Keith's colleagues."
He added: "Policing by its very nature is unpredictable and our officers never know what they will be confronted by when they go on duty. They run towards danger when others run away.
"Our colleagues working in Westminster on 22 March 2017, acted with the utmost professionalism in unprecedented circumstances when confronted by unimaginable evil.
"This bravery must be supported by appropriate numbers of police officers who have the correct training, equipment and back up when required. And we will be working with the force to ensure the lessons are learned from this tragedy."