A massive police operation is under way after a terror attack in Westminster, in the heart of London.
This is what we know so far:
Four people have died - Pc Keith Palmer, 48, mother-of-two Aysha Frade and US tourist Kurt Cochran. The attacker, Khalid Masood, also died.
Masood, 52, had a string of criminal convictions including possession of a knife, but he was not the subject of any current investigations and there was "no prior intelligence about his intent to mount a terrorist attack".
Eight people have been arrested and a number of addresses raided across London, Birmingham and elsewhere.
Those arrested include a 39-year-old woman held overnight at an address in east London on suspicion of preparation of terrorist acts.
A 21-year-old woman and a 23-year-old man were also arrested overnight at an address in Birmingham on suspicion of preparation of terrorist acts.
A 26-year-old woman and three men aged 28, 27 and 26 were arrested overnight at a separate address in Birmingham on suspicion of preparation of terrorist acts.
A 58-year-old man was arrested on Thursday morning at a separate address in Birmingham on suspicion of preparation of terrorist acts.
The woman killed on the bridge was Ms Frade, who worked at DLD College London.
Mr Cochran, 54, from Utah, was the man killed in the incident on the bridge.
Those injured included 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.
Three police officers were also hurt, two of them seriously.
The Hyundai used to mow down pedestrians on Westminster Bridge was hired from a branch of car hire firm Enterprise in Spring Hill, Birmingham.
The attacker was British-born and was investigated by MI5 some years ago over concerns of violent extremism.
The attacker, armed with two large knives, jumped out of the car after smashing it into the railings encircling the Palace of Westminster, fatally stabbing Pc Palmer as he entered the grounds.
He was shot dead moments later by another police officer.
Islamic State has claimed the attacker was one of its "soldiers".
Defence Secretary Sir Michael Fallon has said the working assumption is that the attack is linked to Islamic terrorism.
Prime Minister Theresa May chaired a meeting of the Government's emergency Cobra committee on Wednesday night, later branding the attack "sick and depraved".
Police forces around the UK are reviewing their security arrangements in the wake of the Westminster attack.