He found that the Metropolitan Police had a duty to protect Pc Palmer’s life, under Article 2 of the Human Rights Act, a ruling that could pave the way for his family to sue for damages.

During the inquest, it was revealed that the two armed officers who were on duty that day had been unaware that they were supposed to be positioned at the front gates.

On Wednesday evening, Pc Palmer’s widow, Melissa, accused the Metropolitan Police of failing to be transparent about its failures and said senior figures were still failing to take responsibility.

She 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 to die at a vulnerable location with no protection.

“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.”

She added: “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. They let Keith down by failing to protect him and let us down by failing to investigate his death properly.