An eye-witness to the terrorist attack in New Palace Yard said the assailant pushed the policeman to the floor before “swinging” at him with a knife.
Reporter Patrick Daly’s office overlooks the green in front of Parliament and said he heard a “bang” before “screaming”.
He looked out of his window expecting to see an injured construction worker, but instead saw a “stampede” of people running from Westminster Bridge.
The Parliamentary correspondent for the Bristol Post said he saw the attack unfold, before the assailant was shot to the ground.
He said: “People were running in floods, almost like a stampede, from Westminster Bridge and away from Parliament Square.
“The next thing I saw was one of the policeman who guard the car gate into New Palace Yard being confronted by a man.
“At first, I wasn’t sure if the man was scared and looking for refuge, but then it turned violent.
“The policeman was shoved back and then pushed to the floor, in front of a metal barrier before the green.
“He started lunging at the policeman on the floor.
“It was unclear to me what was being carried in the man’s hands but he made swinging, stab-like motions at the policeman while he lay on the floor.
“It now appears the policeman was being stabbed with a knife.”
He said police ran to help their colleague while another armed officer “slowly” approached the attacker.
“There seemed to be some kind of verbal shouts between them before the armed officer fired off two to three shots causing the attacker to crumple to the floor,” he added.
Patrick said the building is now on lockdown, and he has been asked to stay away from the windows.