Police said the man was in his late twenties, and was detained on a major street between parliament and the residence of Prime Minister Theresa May, on suspicion of committing or instigating acts of terrorism and possession of an offensive weapon.
London's police force said they knew of no immediate further threat as a result of the arrest, and said counter-terrorism officers were continuing their investigation.
The incident comes just over a month after a British-born ploughed a car into pedestrians on nearby Westminster Bridge killing four people before stabbing to death a police officer in the grounds of parliament.
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