The Westminster attacker was British-born and known to the police and intelligence services, the prime minister has revealed.

In a statement to the Commons, Theresa May said he had been investigated some years ago over violent extremism but had been a “peripheral figure”.

“He was not part of the current intelligence picture,” she said.

Eight arrests – at least four of which happened in Birmingham – followed Wednesday’s attack that left four dead.

Those that died are PC Keith Palmer, Aysha Frade who worked at a London college, a man in his 50s and the attacker.

Seven of the injured are still in hospital in a critical condition.

A further 29 had been treated in hospital, Mr Rowley added.

In the attack on Wednesday afternoon, a man drove a car along a pavement on Westminster Bridge knocking down pedestrians, creating panic and leaving dozens injured.

He then ran towards Parliament where he stabbed PC Palmer who was unarmed. Armed police then shot dead the attacker in the grounds.Mrs May paid tribute to PC Palmer saying: “He was every inch a hero and his actions will never be forgotten.”

She also said one of three police officers injured as they returned from an event to recognise their bravery was in a stable condition.

She told MPs, many of whom had been caught up in the commotion: “We will never waver in the face of terrorism.”

PC Keith Palmer and Aysha FradeImage copyrightPA/FACEBOOK

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PC Keith Palmer stopped the attacker in his tracks. Aysha Frade would be deeply missed by all, the principal at the college said

Mrs Frade worked at a London sixth form college just a few hundred metres from Westminster Bridge.

Principal at DLD College, Rachel Borland, said she was “highly regarded and loved by our students and by her colleagues”.