He was held on suspicion of terrorism. A witness said: “He was very calm.”
A joint surveillance operation by Scotland Yard and MI5 led to the 27-year-old being arrested at gunpoint as he walked towards Downing Street.
He was followed every step of the way while he made his way by public transport from an address in South East London to Westminster — where last month five people were killed in a terror attack.
A source said: “It was an extremely tense situation. Nobody could afford to let him out of sight.”
The operation was launched after the man was said to have been reported to authorities by a member of his family several weeks ago, over concerns about his behaviour.
The crop-haired and bearded suspect was believed to have arrived in Westminster on the Tube and Met Police SCO19 firearms officers were called in.
They swooped at a pedestrian central reservation as he crossed Whitehall at 2.22pm.
He was found to have the blades — including a carving knife — in his rucksack.
Witnesses said the man had already pulled one out before he was wrestled to the ground.
Construction worker Zbez Pozdze, 26, said: “He was walking with a knife in his hand, and that’s when the police caught him”.
Chris Kacyk, 40, said he saw the suspect — in a dark tracksuit — reach into a rucksack before someone shouted “armed police” and officers seized him.
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Chris said: “He seemed very calm and collected. He didn’t say anything.
“They shoved him up against the wall and were patting him down.
“I saw his bag on the floor. Police were searching through it and pulled out knives. One was massive, the blade was about 30cm.” Another witness, who works in Parliament, said: “The bloke got to the traffic island, suddenly several plain clothes officers tackled him. Then lots of uniformed coppers turned up.”
Ian Grant, of Poplar, East London, said “They all came from nowhere like a swarm of bees.”
It is feared the suspect may have been planning to stab a police officer — regarded as top targets by ISIS and supporters in the West.
Anti-terror officers had the suspect under surveillance as part of an ongoing operation.
Their investigation was given further impetus by the attacks carried out by 52-year-old Khalid Masood, who drove into pedestrians on Westminster Bridge and stabbed PC Keith Palmer to death.
Yesterday’s suspect was arrested 100 yards from the entrance to Parliament, where the hero cop died. A source said: “Uppermost in everybody’s minds since March 22 has been the prospect of another attack in Westminster. This, we fear, might have been it.”
As well as being closely observed by undercover officers, the suspect was monitored on street CCTV and on the Tube from the Met’s Central 3000 control centre in South London.
Theresa May — who was not at No10 — was briefed on the operation and paid tribute to the police and MI5.
The PM said: “I think it shows that our police and our intelligence and security services are on the alert as they always are, looking to keep us safe and secure.”
The suspect’s identity, nationality and background were not being disclosed as inquiries continued.
He was held on suspicion of planning a terror attack and was last night being questioned at a South London police station.
Brits 'in atrocities'
BRIT jihadis are carrying out regular atrocities in Iraq and Syria, a top US commander claims.
The “foreigners” form the last line of defence as they are more likely to have no qualms about attacking civilians, Col John Dorrian said.
He reckoned fleeing IS leaders were increasingly using the tactic as they lose more territory around the key cities of Mosul and Raqqa.
Col Dorrian said: “Foreign fighters have no reluctance to use scorched earth tactics.
“A lot are very hardcore and they came here to die — they are fighting to the death.”
TERROR fears were raised in Scotland last night after sinister packages containing a mystery white powder were sent to cops and SNP chiefs at five addresses.
Additional reporting: TOM NEWTON DUNN, HARRY COLE and CHRIS POLLARD
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