A Government minister has spoken of the "vivid memories" which haunt him after he tried to save the life of a policeman who was stabbed in the Westminster terrorist attack.
Defence Minister Tobias Ellwood said the hardest part of the day was trying to explain to his eight-year-old son what had happened.
Mr Ellwood, a former soldier, tried in vain to save Pc Keith Palmer, giving him mouth-to-mouth resuscitation and applying pressure to staunch the flow of blood from his wounds after he was attacked outside the Houses of Parliament last March.
The policeman was one of five people killed by Khalid Masood before he was shot dead by a ministerial bodyguard.
In an interview with The Daily Telegraph, Mr Ellwood said: "I think the hardest thing, as well as stepping through with others to try and save Pc Keith Palmer's life, was coming home and finding my eight-year-old boy on top of the stairs having refused to go to bed.
"It was 10 o'clock at night and he was really confused. He couldn't understand why a bad person would do what he did and he also couldn't quite understand why I had then stepped forward in the way that I did.
"I had to explain to him that there are some bad people in this world. There are bad people doing bad things, but there are more good people doing good things, and that's why we stand up to events such as this."
Mr Ellwood, who had previously been reluctant to discuss publicly what happened, said he had decided to speak out after launching a new mental health strategy for the Armed Forces, encouraging veterans to seek help for mental health issues and not to bottle up their experiences.
"What I went through is something... but we shouldn't forget that there are many people who have seen much worse and continue to be affected by it," he said.
"That's why it is so important for us to have the mental health strategy that we need a veterans support package that is understood and a covenant that obliges councils, businesses and communities to recognise the sacrifice that individuals have given."