The Metropolitan police are facing legal action over the death of PC Keith Palmer, murdered during a terrorist attack on parliament.

An inquest in October 2018 concluded with the coroner, Mark Lucraft QC, ruling that the officer’s death may have been prevented had armed officers been closer.

Palmer was on duty on 22 March 2017 at the Palace of Westminster when Khalid Masood ran through a gate and stabbed him.

Palmer, 48, was one of five people killed during the attack that lasted 82 seconds. Masood first ran over people on Westminster Bridge before stabbing the unarmed police officer to death. His rampage ended when he was shot dead by a police officer.

During the inquest the exasperation from Palmer’s widow, Michelle, and his family grew as failings emerged.

PC Keith Palmer was among five people killed in the Westminster attack. Photograph: Metropolitan police/PA

In a statement the Met said it had received a legal letter: “The Met has received a letter of claim in relation to the death of PC Palmer. Given the likelihood of further legal proceedings, we are not discussing any further details at this time.”

The legal letter was first reported by the Daily Mirror.

The inquest’s conclusion from the chief coroner, Mark Lucraft QC, placed blame on 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.”

After the inquest verdict the chasm between Palmer’s grieving family and the Met became clear.

Palmer’s widow, Michelle, who has been left to raise their daughter, Amy, 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.”

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.

Speaking after the inquest verdict, assistant commissioner Neil Basu praised Palmer’s heroism and accepted the coroner’s findings: “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.”