Five people have died, with 50 injured - some critically - in a terror attack near the Houses of Parliament on Wednesday.
Here's everything we know about the victims, the attacker and the police investigation.
Attacker Khalid Masood, 52, killed four pedestrians and injured about 50 others as he mowed down members of the public with a car on Westminster Bridge at about 2:40pm on Wednesday.
He then crashed his hired Hyundai SUV into the railings in front of Parliament Yard before bursting through the gate to the Palace of Westminster with two large knives where he fatally stabbed unarmed Pc Keith Palmer, 48.
He was shot dead moments later by a close protection officer attached to Defence Secretary Sir Michael Fallon.
The attack sent Westminster into lockdown and MPs were forced to stay put in the House of Commons for more than four hours while the area was made safe.
Prime Minister Theresa May had just voted and was standing in members' lobby with other Tory MPs. She was seen being quickly ushered into a silver Jaguar in the grounds of the Palace of Westminster and whisked away to the safety of Downing Street.
Who are the victims?
Three members of the public died following the car rampageon Westminster Bridge. They were mother-of-two Aysha Frade from London, US tourist Kurt Cochran from Utah and Leslie Rhodes, 75, from Streatham, south London.
Pc Palmer and Masood also died despite attempts by paramedics to save them both.
At least 50 people of 12 different nationalities were injured, including 12 Britons, three French children, two Romanians, four South Koreans, two Greeks, and one each from Germany, Poland, Ireland, China, Italy and the United States.
One of the injured has life-threatening injuries and two others are in a critical condition. Three police officers were also hurt, two of whom remained in hospital in Friday with "significant injuries".
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Who was the attacker?
Burly body-building enthusiast Khalid Masood, 52, was born in Dartford in Kent on Christmas Day 1964. His mother Janet Ajao gave birth when she was just 17 years old and brought him up as Adrian Russell Ajao.
The married father-of-three spent years moving round the country - and the prison system - with a host of different identities, including Adrian Elms.
He was most recently based in the West Midlands and had a history of violent knife crime, converting to Islam after years of criminality.
Was he known to police?
He had a string of criminal convictions including GBH, possession of offensive weapons and public order offences, but he had not been convicted of any terrorism offences.
His first conviction was in November 1983 for criminal damage and his last conviction was in December 2003 for possession of a knife.
He was not the subject of any current investigations, and there was "no prior intelligence about his intent to mount a terrorist attack", Scotland Yard said on Thursday.
He was investigated by MI5 some years ago over concerns of violent extremism but was no longer deemed to be a threat.
Masood spent time in Lewes jail, East Sussex, Wayland, Norfolk, and Ford open prison, West Sussex for his offences. There is a good chance he was radicalised in prison.
How many arrested?
Two suspects, both men, remained in custody on Friday night. Seven people have been released with no further police action.
A 32-year-old woman, arrested in Manchester, has been bailed pending further inquiries, while a 39-year-old woman arrested in east London has been released on bail until late March.
Police have seized 2,700 items in searches, including "massive amounts of computer data".
Approximately 3,500 witnesses - including 1,000 from Westminster Bridge and 2,500 from within the Parliamentary estate, have contacted police.
What do we know about the car?
On Thursday, car-hire firm Enterprise confirmed the Hyundai 4x4 used in the attack was one of its vehicles after an employee recognised the number plate in online photos.
The car is understood to have been rented from a branch on the Stratford Road in Shirley, Solihull.
What has Mrs May said about the attack?
Mrs May told the House of Commons on Thursday: "We will never waver in the face of terrorism."
She also said British people have shown terrorists they "will not defeat us" by carrying on with their lives as normal and described the attack as "sickening".
Mrs May said the actions of millions around the country showed terrorists "we will never give in".
In a show of defiance, the PM told a packed Commons chamber: "The greatest response lies not in the words of politicians, but in the everyday actions of ordinary people.
"For beyond these walls today, in scenes repeated in towns and cities across the country, millions of people are going about their days and getting on with their lives."
Paying tribute to Pc Keith Palmer, she said: "He was every inch a hero and his actions will never be forgotten."
Is the capital safe?
Britain's official terror threat remains at "severe", meaning an attack is highly likely.
Mrs May said there was "no reason to believe" further attacks on the public were planned.
Extra armed and unarmed police have been deployed across the capital.
Officers want anyone with images or film of the incident to hand those to the police. They're also asking anyone with information about Masood to call the Anti-Terrorist Hotline on 0800 789 321
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- House of Commons
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- London attack
- Khalid Masood
- Transport for London (TfL)
- Tobias Ellwood
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