Scotland Yard is facing a lawsuit over the death of PC Keith Palmer during the Westminster terror attack.
Coroner Mark Lucraft QC ruled the hero could still be alive if marksmen were stationed with him at the time of the atrocity.
Instead they were 80 yards away when Khalid Masood, 52, stabbed him with two 12in knives at the gates of Parliament in March 2017.
The Met refuses to accept responsibility and PC Palmer’s family said after the inquest senior officers “seem to have closed ranks”.
His wife Michelle added: “He was left at a vulnerable location with no protection to die. [Scotland Yard] let Keith down.”
A Met spokesman confirmed it had received a “letter of claim”.
Lawyers use them to outline the legal basis for the action.
Mrs Palmer’s solicitor refused to comment on the letter.
Masood mowed down Kurt Cochran, 54, Aysha Frade, 44, Leslie Rhodes, 75, and Andreea Cristea, 31, on Westminster Bridge before attacking PC Palmer, 48.
All were “unlawfully killed”,
Mr Lucraft said. He added: “Due to shortcomings, armed officers were not in close proximity to the gates.
"Had they been there they may have been able to prevent PC Palmer suffering fatal injuries.”
