In latest developments:
Prime Minister Theresa May is chairing a meeting of the government's emergency Cobra committee
 
Earlier, a Downing Street spokesman said: "The thoughts of the PM and the government are with those killed and injured in this appalling incident, and with their families."
 
Westminster underground station was shut and remains open for interchange only
 
Home Secretary Amber Rudd urged everyone to remain calm but to be vigilant and if they see anything they were concerned about they should report it to the police
 
A group of French schoolchildren were also on the bridge and three were injured
 
13 students from Edge Hill University in Lancashire were also caught up in the incident - two were taken to hospital and described as walking wounded; two others had minor injuries
 
There are two casualty bureau numbers: 0800 056 0944 and 0207 158 0010 for people worried about family and friends, or eyewitnesses
 
Kings College Hospital says eight patients are being treated there - six male, and two female. Two are critical and two are stable
 
Around 1,000 people were taken to Westminster Abbey for safety and were then being processed by police
 
MPs were locked in the House of Commons for more than four hours and business suspended
 
Parliamentary authorities say both the House of Commons and Lords will sit at their usual times on Thursday
 
Over the following days there will be extra unarmed and armed officers on the streets of London
 
Witnesses say there was what appeared to be a warning shout and then the crack of three or four shots before the attacker fell to the floor.
 
Foreign Office minister Tobias Ellwood - a former Army officer whose brother died in the Bali terrorist bombing in 2002 - attempted mouth-to-mouth resuscitation of an injured police officer.

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