Timeline – How tragic events unfolded...

2.40pm: Emergency services are called to an incident in the area of Parliament Square. It emerges that an attacker, armed with two large knives, mowed down pedestrians with his car on Westminster Bridge then rushed at the gates in front of the Houses of Parliament, stabbing a policeman before being shot dead by other officers.

3.09pm: MPs are told the chamber would “remain in lockdown” until further notice and business is suspended.

3.30pm: Scotland Yard says the attack is being treated “as a terrorist incident until we know otherwise”.

4pm: The first death is confirmed when a junior doctor at St Thomas’ Hospital says one woman has died and a number of others have been hurt - including some with “catastrophic” injuries.

5.40pm: Sources say a police officer stabbed at the Houses of Parliament has died.

6pm: Scotland Yard’s top antiterror officer Mark Rowley confirms four people were killed, including the police officer who was stabbed and his attacker.

8.52pm: Prime Minister Theresa May makes a statement outside Number 10.

10.28pm: Mark Rowley confirms the death toll has risen to five and around 40 people have been injured.

10.30pm: Officer killed in the attack is named as 48-year-old husband and father Keith Palmer.