Halifax MP Holly Lynch was trapped inside the Palace of Westminster during the London terror attack.
Ms Lynch was returning to a meeting in the Shadow Cabinet room following a Commons vote when news of the incident began to filter through.
The group in the meeting barricaded themselves in the room as they heard reports there could be an attacker at large on the Parliamentary estate.
She said: “At one point there was a lot of shouting outside the room which was pretty distressing but I think it was just the police trying to clear the area.”
An armed police officer has died after being stabbed outside the Houses of Parliament.
Two other people have died and at least 20 others are injured after the attacker drove into them in a car on Westminster Bridge.
The alleged assailant was shot and killed by armed police.
It was reported that the attacker, armed with two large knives, mowed down pedestrians with his car on Westminster Bridge, including schoolchildren, then rushed at the gates in front of the Houses of Parliament, stabbing the policeman before being shot dead by other officers.
Ms Lynch is the daughter of a retired police officer and has campaigned strongly over the safety of police and the sentences handed to those who attack officers.
She said: “Having been out with the police in my constituency I am well aware of how hard they work and the risks they face every day.
“I didn’t imagine an officer would have to make the ultimate sacrifice protecting MPs and those who work in Parliament.
“He has the greatest respect of all of us here and our thoughts are obviously with his family.
“We are all going to have to reflect on the safety of the police and the issues this raises more broadly.”
MPs were kept in the Palace of Westminster for several hours until it was safe to evacuate.
It was reported that a primary school from the Calder Valley was on a visit to the Palace of Westminster today but Calderdale councillor Adam Wilkinson tweeted they are understood to be safe.