<sod >Frazer Clarke, 25, from Burton-on-Trent, said: 'We heard a loud bang and screaming and then I noticed some smoke. I thought it was a car crash. 'I looked towards the front gate and people were running, a police officer and a fellow coming to the gate with two knives. 'He was stabbing the police officer with the knives. He was wearing black tracksuit bottoms, a black of grey top and what looked like work boots. The police officer was stumbling and fell on the floor'.        This was the series of events this afternoon where a knife attacker drove into pedestrians before he was shot by police The Hyundai 4x4 used by the attacker remains at the scene after it slammed into a fence before the attacker got out  Armed Police have opened fire and shot a person outside the Houses of Parliament.< eod>< sod > Frazer Clarke, 25, from Burton-on-Trent, said: 'We heard a loud bang and screaming and then I noticed some smoke. I thought it was a car crash. 'I looked towards the front gate and people were running, a police officer and a fellow coming to the gate with two knives. 'He was stabbing the police officer with the knives. He was wearing black tracksuit bottoms, a black of grey top and what looked like work boots. The police officer was stumbling and fell on the floor'.        This was the series of events where a knife attacker drove into pedestrians before he was shot by police The Hyundai 4x4 used by the attacker remained at the scene after it slammed into a fence before the attacker got out  Armed Police opened fire and shot the attacker outside the Houses of Parliament.< eod>