Buckingham Palace was in lockdown on Friday night after a man armed with a knife injured two police officers.
The 26-year-old suspect was tackled by officers at the scene on the Mall and held on suspicion of grievous bodily harm and assault on police.
Early on Saturday morning the Metropolitan Police said the suspect had been further arrested under the Terrorism Act.
“Officers at the Mall spotted a large knife in his vehicle and went to arrest him. During the course of detaining the man, two male police officers suffered minor injuries to their arm.”
Two officers sustained minor injuries as they restrained the suspect and were treated in hospital. They were later discharged. No other people were injured.
The suspect was taken to a London hospital for treatment of minor injuries before being moved to a central London police station for questioning.
Police said the man was arrested at the top of the Mall, close to the palace gates, in possession of a knife at around 8.35pm.
The Queen was not in residence at the time of the security scare. She is at Balmoral Castle in Scotland and other senior members of the Royal family are also on holiday. It is understood that no members of the Royal family were in Buckingham Palace at the time.
A Buckingham Palace spokesman said it did not comment on security issues.
Witnesses said the man was removed from a car, having apparently driven his vehicle towards them.
“We turned up and there was one police van and one car, there was also a civilian’s car that had veered towards the police car,” said Kiana Williamson.
“They were trying to get the man out of the car, shouting, more police were arriving on to the scene and the man was fighting back.
“I saw one injured policeman with an injury to his arm although it didn’t look severe.”
The area was surrounded immediately by armed police and other security services and tourists were ushered away from the area.
There were unconfirmed reports on social media that the man was carrying a sword or machete.
Leonardi Paoli, wrote on Twitter: “Buckingham Palace in lockdown. Man with a sword attacked an officer.” He claimed that he had overheard police talking about a “sword attack”, although police would only confirm that the man had a knife.
The police response to the incident was rapid, and the area was soon secured by dozens of officers and police vehicles.
“Stuck outside Buckingham Palace with many armed police officers. Heavy rifles on display traffic at a halt,” said Amir Jan Malik.
The Buckingham Gate and Wellington Arch entrances to the palace were sealed off last night and several pairs of armed officers were seen stationed at checkpoints around the palace.
Birdcage Walk and The Mall – the roads running around St James’s Park – were closed.
Europe is on high alert following a spate of recent terror attacks. A terror cell launched an attack on Barcelona’s famed Las Ramblas street last Wednesday, and at a nearby seaside town, leaving 14 people dead.
Last night in Brussels, a man armed with a machete attacked a group of soldiers. He has shouted “Allahu Akbar” during the attack, officials said. He was shot dead at the scene, while the two soldiers were not seriously injured.
Belgian officials said they had “neutralised” the man and that the “situation is under control”.
There have been several terror attacks in Britain this year alone.
In March, a terrorist drove a car into pedestrians on Westminster Bridge, killing four people. Khalid Masood then ran into the grounds of the Palace of westminster, where he fatally stabbed an unarmed police officer. He was shot dead by an armed officer.
A concert by pop star Ariana Grande in Manchester was attacked by a terrorist in May. Suicide bomber, Salman Ramadan Abedi, detonated a shrapnel-laden homemade bomb at the entrance to the concert, leaving 23 adults and children dead and 250 injured.
In June, three terrorists in a van drove into pedestrians on London Bridge. They then ran to Borough Market, where they stabbed people enjoying their evening out. In total eight people were killed. The three terrorists were shot dead by police.