But for one MP who was hailed for her bravery amid chaotic, confusing and horrifying scenes, there was at least a sliver of a silver lining in that it improved the much maligned culture in Parliament.
Despite the recent slew of bullying claims, Mary Creagh said MPs from all parties from around the country, police, staff and other workers in the Palace of Westminster have a stronger sense of solidarity since experiencing the trauma of a terror attack together.
The Wakefield MP told The Yorkshire Post: “Whether from the most senior MP to the most straightforward worker in Parliament, everybody experienced what it was like, and so there’s a kinder atmosphere.
“I know this runs counter to the bullying narrative, but actually every morning I talk to the police officers on the gate, I didn’t used to do that, every day I say hello to the armed police officers guarding the Westminster entrance, I didn’t used to do that.
“People take the time to treat the officers, the security staff, but also the people who serve the food (well).
“I think it’s changed how we relate to each other as people and it’s changed it for the better.”
The day itself is “etched very clearly” in her mind - she was on her way to vote in the Commons when she was confronted with Conservative Minister Penny Mordaunt running towards her in high heels shouting “get back, someone’s been shot” - it was Khalid Masood, shot dead by police in New Palace Yard after ploughing into pedestrians on Westminster Bridge before fatally stabbing unarmed officer Keith Palmer.
“It was one of those moments where you don’t stop to say ‘is she telling the truth?’ because it’s definitely the truth”, Ms Creagh said.
The Labour former frontbencher and others were left banging on an exit door which led into Westminster Underground station, demanding to be let out, before a policeman defied his orders to allow them into the Tube.
Once there, Ms Creagh’s first thought was not to run away, but to urge control room staff to shut the station down to protect Tube passengers from the carnage just yards away, for which she was honoured by leading rail union TSSA with a life membership for her courage.
Five innocent people were killed in Masood’s rampage - 48-year-old Pc Palmer, who was on duty at the Palace of Westminster, along with US tourist Kurt Cochran, Romanian tourist Andreea Cristea, 31, and Britons Aysha Frade, 44, and 75-year-old Leslie Rhodes, who were mown down on the bridge.
Ms Creagh said: “There was the worst of humanity, one misguided ideologist caused all that carnage and killed five people, their lives were stolen from them by him.
“But what it also showed was how we respond is all about the best of humanity, it’s about people reaching out to strangers, people caring for each other, people coming together in solidarity.”
Tributes to murdered police officer
The unarmed constable murdered in the Westminster Bridge terror attack was “a proud and courageous police officer who did his job and never wanted any fuss”, his friend has said.
Pc Shaun Cartwright paid tribute to Keith Palmer, who was killed as he stood guard at the Palace of Westminster on March 22 last year.
In a statement released through Scotland Yard he said: “Keith loved being a police officer, he just wanted to help people and do his best.
“Keith was always happy, always the first to help anyone out, first in to work and the last one out.
“Keith was a true and loyal friend, utterly reliable.”