An MP has described hearing "shouting" from outside the Houses of Parliament moments before the building was put into lockdown.
A policeman was stabbed and his attacker shot by officers during the incident inside the gates of the Palace of Westminster on Wednesday (March 22) afternoon.
Gunshots were heard at the scene just after 2pm.
London Ambulance Service has since declared a major incident, with an air ambulance and paramedics sent to the scene.
Mr Lord added: "We had just been voting and I popped into the tea room between votes when I saw on the screens a message saying 'sitting suspended'.
"We put on the televisions to see what was happening.
"I heard shouting outside in the courtyard, which I think was the police or security services telling people what to do.
"We have been told to sit tight until further notice. My staff are safely in the office working."
He added that a lot of MPs were in the chamber and division lobbies.
"A lot of the MPs are just locked in the chamber, as it were," Mr Lord said. "We are just waiting for further instruction.
"Everyone is calm and we are very interested to know what's happened but there is some anxiety.
"Everyone has been making sure their staff are all there and accounted for."
Spelthorne MP Kwasi Kwarteng confirmed he was sat in his office on lock down and awaiting further information.
"I heard nothing because I was in the old part of the palace and I didn't see anything either," he said.
"We're relatively calm here, I wouldn't say people are panicking - we are more just puzzled as to what is going on because we haven't been told very much.
"We are just trying to piece bits of information together."