How events unfolded in the Westminster attack:
* Emergency services are called at 2.40pm local time 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.
*MPs are told the chamber will remain in lockdown until further notice and business is suspended.
* At around 3.30pm Scotland Yard says the attack is being treated "as a terrorist incident until we know otherwise".
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* The first death, of a woman, is confirmed after 4pm and it's confirmed a number of others have been hurt, some "catastrophically".
* At about 6pm, Scotland Yard's top anti-terror officer Mark Rowley confirms four people were killed, including the police officer who was stabbed and his attacker.
* At 6.45pm a spokesman for 10 Downing Street says Prime Minister Theresa May will chair a meeting of the Government's emergency Cobra committee to discuss an immediate response.
* In a late-night statement after the Cobra meeting May describes the attack as "sick and depraved" but vows Londoners will never give in to terror.
* At 10.30 counter-terrorism chief Mark Rowley says the death toll has risen to five with forty people injured. He says police believe they know the identity of the attacker but are not immediately commenting.
