- Video report by ITV News Security Editor Rohit Kachroo
A man detained after a suspected terror attack outside the Houses of Parliament has been further arrested on suspicion of attempted murder.
Salih Khater, 29, a UK national of Sudanese origin, was arrested on suspicion of terror offences after the silver Ford Fiesta he was driving collided with cyclists and pedestrians before crashing into a security barrier just before 7.40am on Tuesday.
Khater told members of the Sudanese community he was travelling to London to obtain a visa to visit his homeland, officials at a Birmingham mosque have said.
Scotland Yard announced on Wednesday that he had been further arrested on suspicion of attempted murder.
Police also confirmed that they had obtained a warrant to detained the suspect for a longer period of time.
It comes after police searched three addresses in the Midlands in the wake of the attack.
Detectives believe the privately-owned car was driven from Birmingham late on Monday night, arriving in London just after midnight.
Counter-terrorism officers are carrying out searches at two addresses in Birmingham and a residential property in Nottingham as part of the probe.
Plain-clothed police officers could be seen outside an address in Peveril Street in Nottingham. Neighbours have said the house - which is shared by six occupants - is home to six Sudanese people.
Plain-clothed officers were also seen at an address in Stratford Road, Birmingham.
The Metropolitan Police said they are treating the crash as a terrorist incident and their counter-terrorism officers are leading the investigation.
Scotland Yard said the vehicle was driven around the Westminster area from around 6am - more than an hour-and-a-half before the crash - having been in the Tottenham Court Road area between 1.25am to 5.55am.
A spokesman added: "It was then driven around the Westminster and Whitehall area from approximately 6am and stayed in this area until the time of the incident."
Scotland Yard said no one else was in the vehicle at the time of the crash and no weapons have been recovered.
Home Secretary Sajid Javid has said people "must keep an open mind" about the incident.
He said: "The briefing I have received from counter-terrorism police and the security services is that work is ongoing and they are doing everything they can to find out more about the incident.
"We must keep an open mind about what has happened and I'm sure when they do have more information they will say more."
The suspect has not been formally identified and his motives are not currently known, although Metropolitan Police Assistant Commissioner Neil Basu said it is not believed he was already known to police or MI5 and that the attack "appeared to be deliberate".
Mr Basu, who leads counter-terror policing in the UK, said that no other suspects have been identified and there is nothing to suggest that the public are in danger, but he urged people to remain "vigilant".
Prime Minister Theresa May praised the "formidable courage" of the emergency services who "ran towards a dangerous situation in order to protect the public".
She added: "The twisted aim of the extremists is to use violence and terror to divide us. They will never succeed."
Specialist police officers from Project Servator, who are trained to recognise when a person is displaying minute signs of anxiety, have been deployed in Westminster to identify anyone who may be in the area for terrorist or other criminal purposes.
London Ambulance Service (LAS) said they treated three people at the scene and following this took two of them to hospital.
A man suffered "non-serious" injuries and a woman, "serious, but not life-threatening injuries". Both have been discharged from hospital.
An eyewitness said that cyclists were among those injured, while another said that the car has been travelling "at speed - at least 50mph" when it appeared to "deliberately" crash into the barriers.
Jason Williams, 45, from Kennington, was walking to work when he saw the "car going at high speed towards Parliament...
"It looked deliberate. It didn't look like an accident. How do you do that by accident? It was a loud bang."
Geoffrey Woodman, a strategy consultant from Battersea, had stopped at the traffic lights by Parliament Square on his cycle to work when he heard tyres screeching and the car swerved into cyclists and towards the security barriers.
"This car turned round to the left and swerved into the wrong lane of traffic and into the bank where all the cyclists wait."
He said most people managed to jump off their bikes to safety but one woman who "seemed in some distress" was clipped by the bonnet of the car as it passed.
Mr Woodman said paramedics from a passing ambulance stopped to help before armed police arrived on the scene.
In footage aired by the BBC, the car is seen coming along the road next to Parliament Square before moving to turn right towards Westminster Abbey.
As an ambulance passes the car on its right-hand side, the vehicle swerves left, crossing oncoming traffic and a pavement before entering a small road and crashing into a security barrier.
A police officer can be seen jumping another barrier that runs along the side of the road to get away.
Mr Basu said the car was not being pursued by police and although the incident appeared to be "deliberate" he "could not comment" on the driver's motives, and whether the police officers were targeted.
Cordons around the area have now been lifted, although the area immediately around where the crash took place remains sectioned off.
A meeting of the Government's emergency Cobra committee was held at 2pm, however, it was a meeting of officials, with no cabinet ministers attending.
The Prime Minister is currently away in Switzerland on the second leg of her summer holiday, but said that her "thoughts are with those injured" and praised the "formidable courage" and professionalism of the emergency services who "ran towards a dangerous situation in order to protect the public".
Theresa May added that the UK's terror threat level remains at severe.
Mrs May also urged "the public to remain vigilant but also to come together and carry on as normal, just as they did after the sickening attacks in Manchester and London last year.
"The twisted aim of the extremists is to use violence and terror to divide us.
"They will never succeed."
Home Secretary Sajid Javid also thanked the emergency services and said his thoughts too, were with the injured.
Mayor of London Sadiq Khan said he "utterly condemned" the attack.
"All Londoners, like me, utterly condemn all acts of terrorism on our city," he said.
"The response of Londoners today shows that we will never be cowed, intimidated or divided by any terrorist attack...
"My heartfelt thanks goes to the brave first responders who were so quickly on the scene following the attack."
US President Donald Trump was quick to tweet that "another terrorist" attack had occurred in London, adding that "toughness and strength" were required.
Forensics officers have begun investigations at the scene where the car remains.
Londoners can expect to see an increased police presence on Tuesday in the aftermath of the incident.
ITV News Political Correspondent Paul Brand, who was near to the scene of the crash said it appeared that the "car has ended up in quite a specific spot, down what is effectively a slip road to leave the main road and enter the car park for the House of Lords".
Another witness at the scene, Ewalina Ochab, said that the crash "looked intentional - the car drove at speed and towards the barriers...
"I saw a silver car driving very fast close to the railings, maybe even on the pavement."
Ms Ochab continued that the car did not appear to have a front registration plate.
The Houses of Parliament are surrounded with security barriers of steel and concrete.
The measures were extended in the wake of the Westminster Bridge attack in March 2017 when Khalid Masood ploughed a car into crowds on Westminster Bridge, killing four people.
Masood abandoned his car then stabbed and killed unarmed Pc Keith Palmer before he was shot by armed police in a courtyard outside Parliament.
In addition to five terror attacks which happened last year, authorities say they have stopped 13 Islamist and four extreme right-wing plots since the Westminster atrocity in March 2017.
Police and MI5 are running at least 676 live counter-terror operations involving roughly 3,000 active "subjects of interest" - while there is also a wider pool of more than 20,000 individuals who have previously featured in probes whose threat must be kept under review.