Police have named the man thought to be responsible for the attack in Westminster yesterday as Khalid Masood.
Masood, 52, was born in Kent and detectives believe he was most recently living in the West Midlands.
Scotland Yard said Masood had previous convictions for assaults, including 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.
Masood was also known by a number of aliases, the Metropolitan Police said.
Earlier today, Prime Minister Theresa May said the attacker was born in Britain and had previously been investigated for violent extremism.