The Met Police is facing legal action in regards to the murder of PC Keith Palmer in the Westminster terror attack.
PC Palmer was stabbed by terrorist Khalid Masood during the attack in March 2017.
At an inquest in October 2018 chief coroner Mark Lucraft QC found shortcomings in security at the Palace of Westminster.
Masood ploughed into pedestrians on Westminster Bridge before stabbing Pc Palmer.
He was eventually shot dead by a plainclothes close protection officer.
Scotland Yard said in a statement: “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 force would not discuss who has made the claim, which was first reported by the Daily Mirror.
After a four-week inquest at the Old Bailey, Mr Lucraft QC 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 Mrs Palmer issued a statement, on behalf of her and daughter Amy.
This 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.”
Assistant commissioner Neil Basu apologised on behalf of the Met and said the lost chance to save a “brave and courageous officer” was unacceptable.
Mr Lucraft found that Pc Palmer, American tourist Kurt Cochran, 54, retired window cleaner Leslie Rhodes, 75, mother-of-two Aysha Frade, 44, and Romanian designer Andreea Cristea, 31, were unlawfully killed.