The widow of a police officer who was stabbed to death in a terror attack outside the UK parliament is to sue Scotland Yard over their failure to protect him. PC Keith Palmer,48, was one of five people murdered by Khalid Masood in the Westminster Bridge terror attack in London in 2017. Masood had driven a vehicle at pedestrians before arming himself with two 12inch knives and attacking PC Palmer inside the grounds of the Palace of Westminster. PC Palmer's wife Michelle is now to sue the Metropolitan Police force over its failure to protect him. An inquest ruled in 2018 he could still be alive if firearms officers had been closer. The inquest was told that the nearest armed officers were 80 yards away. Two years prior to the attack, a senior officer had raised concerns about the positioning of marksmen around the venue. Scotland Yard has apologised to PC Palmer's family but has not admitted liability for his death. Mrs Palmer has criticised the force for leaving her husband on guard on his own. “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?," she has said in a statement. “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.” The UK security services have also being accused of failing to monitor Masood. The inquest had found that Masood's association with extremists dated back 14 years but security services had concluded he did not pose a major threat. In the inquest, Mark Lucraft QC, the chief coroner, ruled that “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.” Scotland Yard has declined to comment on the legal case. In 2018, it said it accepted the findings of the coroner and said that security arrangements had been substantially changed in the wake of the killings. Following the inquest, Assistant Commissioner Neil Basu had said: "For the loss of that possibility to protect him from Khalid Masood, we are deeply sorry.” American tourist Kurt Cochran, 54, retired window cleaner Leslie Rhodes, 75, Aysha Frade, 44, and Romanian tourist Andreea Cristea, 31, were killed after they were hit by Masood’s car on Westminster Bridge. A further 29 people were left seriously injured. After the attack on PC Palmer, Masood was shot dead as he ran at two protection officers.