I was walking back to The Independent’s office in Parliament with some birthday chocolates for a colleague, when terror struck.

All around me were MPs heading off to the chamber to vote. Behind me Michael Gove was discussing changes to school funding with a worried Conservative MP.

Suddenly, I heard shouting from outside Westminster Hall to my right, quickly followed by at least two gunshots, maybe more.

Video shows terrifying moment police open fire outside parliament

Turning my head, I saw a police officer fall to the ground, clutching his arm or his shoulder.

In the confusion, as shouts and screams rang out around me, it appeared the officer had been shot, although we later learned he had been stabbed.

I saw his attacker running towards Parliament’s main gates, trying to escape it seemed, but he was quickly cut down by the shots from other police officers.

There were shouts before the shots came – a warning for the man in dark clothes to drop his weapon, presumably – but it was ignored and he paid the price.

As the man lay motionless, other officers rushed to usher away a large crowd standing outside Westminster Hall, just a few yards from the violence.

In pictures: Westminster attack Show all 9 1 /9 In pictures: Westminster attack In pictures: Westminster attack An air ambulance lands after gunfire sounds were heard close to the Palace of Westminster in London PA wire In pictures: Westminster attack MPs wait until the situation is under control in Westminster. 'The alleged assailant was shot by armed police,' David Lidington, leader of the House of Commons, told the house. BBC News In pictures: Westminster attack Crowds gather in Westminster after shooting incident, which police are treating as terror attack BBC News In pictures: Westminster attack Police were also called to an incident on Westminster Bridge nearby AP In pictures: Westminster attack Early reports indicate the car, which mounted the pavement on Westminster Bridge and mowed into around a dozen people, was the same vehicle which then rammed into the railings of the Palace of Westminster, just around the corner Reuters In pictures: Westminster attack Security sources described the suspected assailant as a middle-aged Asian man, who is understood to have left the car before attacking a police officer with a seven-to-eight inch knife PA wire In pictures: Westminster attack Police have asked people to avoid the immediate area to allow emergency services to deal with the ongoing incident AP In pictures: Westminster attack One woman has died and a number of others, including the police officer, have been hurt, according to a junior doctor at St Thomas' Hospital Reuters In pictures: Westminster attack At least three gun shots were heard by those inside Westminster, and proceedings in the House of Commons have been suspended AP

Some MPs started to ask me what was going on, while others rushed away as the severity of the incident started to become clear. Then we were ordered to follow them.

Back in the office, I and other reporters watched from the window overlooking New Palace Yard as paramedics tended to the stricken officer.

A few yards away, it seemed clear that his attacker was fighting for life, a paramedic kneeling over him furiously pumping his chest over-and-over again to keep his heart going.

As we watched, Parliament went into lockdown and the Commons was suspended as disbelieving MPs were told what had happened outside the supposedly super-secure Palace of Westminster.

“There has been a serious incident within the estate,” Commons Leader David Lidington said. “It seems that a police officer has been stabbed, that the alleged assailant was shot by armed police.

”An air ambulance is currently attending the scene to remove the casualties.”