The suspect held over the Westminster terror crash was in the capital to get a Sudanese visa, Sky News understands.
Salih Khater - a British citizen of Sudanese origin - had his papers with him and was trying to apply for a visa via the Sudanese embassy, trustee of Birmingham central mosque Nassar Mahmood said.
The 29-year-old suspect was not known as "fervent worshipper" in Birmingham, Mr Mahmood added.
Police have been granted a warrant to hold Khater in custody until Monday after his arrest on suspicion of preparing an act of terror.
He has also been arrested on suspicion of attempted murder.
A Facebook page for a man of the same name as the suspect says he lives in Birmingham, works as a shop manager, and has studied at Sudan University of Science and Technology.
Police concluded their searches of two addresses in Birmingham and one in Nottingham on Wednesday morning.
They continue to search a third address in Birmingham, after a car smashed into barriers near Parliament on Tuesday morning.
The Met confirmed he is a UK national of Sudanese origin.
Officers revealed the driver travelled from Birmingham to London on Monday night and arrived in the capital just after midnight.
He remained in the Tottenham Court Road area, close to Oxford Street, from around 1.25am until 5.55am.
The silver Ford Fiesta was then driven to Westminster and Whitehall for about 6am and stayed in the area until the time of the attack.
It hit cyclists and pedestrians at 7.37am before crashing into security barriers.
The suspect was unknown to MI5 and "not currently cooperating", the Metropolitan Police said afterwards.
His vehicle was removed late on Tuesday night.
A man and a woman were taken to hospital with non life-threatening injuries after the vehicle hit cyclists in rush hour, but they have now been discharged.
Another man was also treated at the scene.
Witnesses have described how the car came "whipping round the corner" and drove through about a dozen cyclists.
Robert Nicholson told Sky News he saw the incident unfold as he was waiting in a "safe cycling box" near Parliament.
He chased the car after the impact left one woman flying up "onto the bonnet" and snapped the frame of one of the bikes.
Met Police Assistant Commissioner Neil Basu said: "There is no intelligence at this time of further danger to Londoners or to the rest of the UK connected to this incident."
Project Servator officers, specially trained to recognise anyone displaying subtle signs of anxiety, have been deployed in Westminster to identify any other potential attackers.