The man being held on suspicion of terrorism after the Westminster car crash has been named as Salih Khater by government sources.
The 29-year-old British citizen, originally from Sudan, is being questioned in south London.
Police have been searching three addresses in Birmingham and Nottingham as part of their investigation.
Three people were injured after the vehicle hit cyclists and pedestrians during Tuesday morning’s rush hour.
The suspect is not believed to have been known to MI5 or counter-terrorism police, but is understood to have been known to local police.
He did not co-operate with officers after his arrest, Scotland Yard said.
