LONDON (AFP) - The eight people arrested following the attack outside the British parliament are being investigated "on suspicion of preparation of terrorist acts," police said on Thursday (March 23).

They also said that five people remained in critical condition and two more had life-threatening injuries after the attacker ploughed into pedestrians on Wednesday before stabbing a policeman and being shot dead.

Police named the attacker as 52-year-old Khalid Masood, who had a string of convictions but none of them terror-related.

The eight arrested included two women and five men arrested at three addresses in the central city of Birmingham and a woman arrested in London.

The police statement said that there had also been a raid in Wales in which no arrests were made.

"Detectives are continuing to search" the sites that were raided, the police said.

It said the seven arrested in Birmingham were being held under the Terrorism Act, which allows for longer detention times before charging.