The man believed to have carried out the attack in Westminster has been named by police as Khalid Masood.
Kent-born Masood, who died in the attack, was not the subject of any current police investigations, but had a range of previous convictions.
The 52-year-old was believed to have been living in the West Midlands.
The so-called Islamic State group has said it was behind the attack, in which PC Keith Palmer, Aysha Frade and US tourist Kurt Cochran were killed.
Eight arrests were made in London and Birmingham following Wednesday’s attack.
Masood drove into pedestrians on Westminster Bridge before crashing his car into railings and then running into the grounds of Parliament, armed with a knife. He stabbed PC Palmer and then was shot dead.
Police said there had been no prior intelligence about his intention to carry out an attack.
But he was known to the police and his previous convictions included GBH, possession of offensive weapons and public order 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 had not been convicted of any terrorism offences.
Car hire company Enterprise said the vehicle used in the attack had been rented from its Spring Hill depot in Birmingham.
The BBC understands Masood had hired the Hyundai SUV in person, giving his profession as a teacher.
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PC Palmer, who was stabbed in the grounds of Parliament, was a 48-year-old father.
He was an unarmed member of the parliamentary and diplomatic protection squad, with 15 years’ service.
His family said in a statement that he would be remembered as a “wonderful dad and husband”.
They also described him as “a loving son, brother and uncle. A long-time supporter of Charlton FC. Dedicated to his job and proud to be a police officer, brave and courageous. A friend to everyone who knew him.
“He will be deeply missed. We love him so much.
“His friends and family are shocked and devastated by his loss and ask that they are left to grieve alone in peace.”
A JustGiving page set up for the family of PC Palmer reached its target of £100,000 on Thursday afternoon, less than 24 hours after it had been set up. That target has since been doubled.
Mrs Frade worked at a London college, while Mr Cochran was from Utah, in the US, and had been visiting the capital with his wife Melissa, who is in hospital with serious injuries.
According to a family statement, the couple had been celebrating their 25th wedding anniversary and were due to return to the US on Thursday.
Mrs Frade and Mr Cochran were killed on Westminster Bridge.
In other developments:
- The Queen said her “thoughts, prayers, and deepest sympathy” are with all those who have been affected by the “awful violence”
- A candlelit vigil will be held in Trafalgar Square in central London on Thursday evening
- MPs held a minute’s silence before Parliament continued business as normal
- Prime Minister Theresa May spent 40 minutes visiting the injured in hospital
- People worried about family and friends can call the police casualty bureau on: 0800 056 0944 or 0207 158 0010. Anyone with images or footage of the incident can send them to ukpoliceimageappeal.co.uk
Seven of those injured by Masood are still in hospital in a critical condition. A further 29 were treated in hospital, police said.
In the Commons on Thursday, Mrs May paid tribute to PC Palmer saying: “He was every inch a hero and his actions will never be forgotten.”
She told MPs, many of whom had been caught up in the commotion on Wednesday: “We will never waver in the face of terrorism.”
An emotional James Cleverly MP asked Mrs May to consider recognising posthumously the “gallantry and sacrifice” made by PC Palmer, who he had known from his time in the Army.
Mrs Frade worked at a London sixth-form college just a few hundred metres from Westminster Bridge.
The principal at DLD College, Rachel Borland, said she was “highly regarded and loved by our students and by her colleagues”.
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Mrs May said 12 Britons had been admitted to hospital and other victims included three French children, two Romanians, four South Koreans, one German, one Pole, one Irish, one Chinese, one Italian, one American and two Greeks.
Thierry Terret, who is in charge of schools in Brittany, said the three injured students were not in a life-threatening condition and were on their way home.
Earlier, Acting Deputy Commissioner Mark Rowley said seven arrests had been made during raids in London and Birmingham – an eighth was announced several hours later.
The BBC understands that searches and arrests have been carried out in Forest Gate, east London, Wales, Surrey and Sussex, as well as in Birmingham.
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