British counter-terrorism police are carrying out three searches in central England as part of an investigation after a car slammed into barriers outside the Houses of Parliament in London.

Police say the driver, a 29-year-old UK national, was arrested on suspicion of preparing a terrorist act. He is currently being questioned at a south London police station.

Police say the silver Fiesta, which was privately owned, had travelled from Birmingham to London yesterday.

It was then driven around the Westminster and Whitehall area from approximately 6 am local time until the crash at 7.37 am local time.

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Police say there have been no other arrests in connection with this investigation.

Britain's Government has kept its threat level for terrorism at severe.

The decision not to elevate the threat level followed a meeting of the Government's emergency committee. Assistant Commissioner Neil Basu of the Metropolitan Police has said no other suspects have been identified and police believe there is no further threat to Londoners.

Prime Minister Theresa May urged the country to come together and carry on as normal, even as she urged the public to "remain vigilant"

British authorities say they have foiled 13 Islamic extremist plots and four far-right plots since March 2017, and currently have 676 live counterterrorism investigations.

British police say the crash appears to be deliberate. They are treating is as an act of terrorism, but they have yet to determine the driver's motive.

Police say they are lifting cordons that had sealed off much of London's Westminster government district.

The Metropolitan Police force says cordons are being lifted apart from a stretch of road around the scene.

Forensics officers in coveralls can be seen collecting evidence from the silver car, which plowed into pedestrians and cyclists before striking a barrier outside Parliament.

US President Donald Trump has called a crash outside Britain's Parliament "another terrorist attack in London."

Trump tweeted: "These animals are crazy and must be dealt with through toughness and strength!"

- AP

The silver car crashed into security barriers outside the Houses of Parliament in London.
The silver car crashed into security barriers outside the Houses of Parliament in London.