Top anti-terrorism officer says Met is urgently investigating whether there was ‘assistance or support’ for attack that left seven dead and 21 in critical condition

Investigators are racing to find out how Britain’s counter-terrorism defences were breached for the third time in 10 weeks, as police mounted multiple raids and arrested a dozen people following the London Bridge attack.

Britain’s top anti-terrorism officer, Metropolitan police assistant commissioner Mark Rowley, said detectives were urgently investigating to discover if the three men who killed seven people and left 21 in a critical condition on Saturday night by running over pedestrians in a rented van and stabbing people in Borough Market were “assisted or supported”. The attack was stopped when eight armed officers killed them in a hail of about 50 bullets, fearing it was a “life or death situation”.

Police respond to incidents at London Bridge and Borough Market – live Read more

Armed police raided homes in Barking, east London, on Sunday, including the home of one of the suspected attackers who neighbours described as a married father of two young children who regularly attended two local mosques.

Five people – four men and a woman – were taken by armed police from the apartment block where he was believed to have lived. Three women were led away from the same flats and police raided a flat above a bookmakers on Barking Road.

“Work is ongoing to understand more about [the three attackers], about their connections and about whether they were assisted or supported by anyone else,” said Rowley.

Play Video 1:23 One member of the public ‘caught in police crossfire’ during London attack – video

He would not comment on whether or not the attackers were known to the police or intelligence services, citing ongoing efforts to confirm their identities.

However, a woman who lives in the block that was raided told the Guardian she had expressed concerns to Barking police about the man’s extremist opinions. Erica Gasparri said she had gone to the police two years ago after she feared the man was radicalising children in a local park.

“I took four photographs of him and gave them to the [local] police,” Gasparri said. “They rang Scotland Yard when I was there and said the information had been passed on. They were very concerned.

“They told me to delete the photos for my own safety, which I did, but then I heard nothing. That was two years ago. No one came to me. If they did, this could have been prevented and lives could have been saved.”

Police believe all the attackers were killed in what Rowley described as a “critical” confrontation given that the terrorists were wearing what appeared to be suicide belts, but turned out to be hoaxes.

“I am not surprised that faced with what they must have feared were three suicide bombers, the firearms officers fired an unprecedented number of rounds to be completely confident they had neutralised those threats,” he said. “I am humbled by the bravery of an officer who will rush towards a potential suicide bomber thinking only of protecting others.”

One official confirmed that police and MI5 had been reviewing a large pool of 20,000 former terrorism suspects to see if they needed to be reassessed.

Rowley said additional police, armed and unarmed, would be placed on patrol in the capital, policing plans for forthcoming events would be reviewed and “increased physical measures” would be used in order to keep the public safe on London’s bridges.

On Sunday night, 36 people remained in hospital after the attack. One of the dead was a Canadian, another was French, while the injured included several other French nationals, two Australians and two New Zealanders.

The Canadian victim was named as Christine Archibald, who worked in a homeless shelter until she moved to Europe to be with her fiance. Her family said in a statement: ““We grieve the loss of our beautiful, loving daughter and sister. She had room in her heart for everyone and believed strongly that every person was to be valued and respected. She would have had no understanding of the callous cruelty that caused her death.”

Two police officers were also injured. They were an on-duty member of the British transport police armed only with a baton who was stabbed in the face and head when he confronted an attacker and an off-duty member of the Metropolitan police. One member of the public was hit by a stray bullet and was hospitalised but their injuries are not life-threatening.

Witnesses told the BBC that the attackers shouted “this is for Allah” before launching assaults with knives and blades said to be 10 inches long.

Elizabeth O’Neill, the mother of one of the victims, 23-year-old Daniel O’Neill, who was being treated in King’s College hospital, said: “A man ran up to him and said: ‘This is for my family, this is for Islam,’ and stuck a knife straight in him. He’s got a seven-inch scar going from his belly round to his back.”

Gabrielle Sciotto, a documentary maker who was on the scene, said the terrorists were fleeing a policeman who was chasing them out of Borough Market when they were shot.

“They ran towards me because the police officer was trying to chase them,” he said. “Suddenly lots and lots of police came from the other direction. There was a lot of shouting: ‘Stop, stop, get on the floor.’ Then the police shot them.”

Facebook Twitter Pinterest A picture that has been circulating showing a man on the ground, apparently with canisters strapped to his body. Photograph: Gabriele Sciotto

Before that, members of the public had fought back. Gerard Vowls, 47, said he saw a woman being stabbed by three men in their 30s and threw chairs, glasses and bottles in an attempt to stop them. “They kept coming to try to stab me,” he said. “They were stabbing everyone. Evil, evil people.”

Sciotto took photographs of the dead terrorists, which allowed neighbours of one suspected attacker at a modern apartment complex in Barking to identify him.

“He lived here for about three years. I used to see him with his wife in a burka,” said one woman who asked not to be named. “She was pregnant but recently had a baby and they had a small boy of about two. There was a succession of unusual cars coming and going here in the last while. There was a foreign-registered BMW which was just stacking up [parking] tickets. Then in the last week the activity stopped.”

“He used to play with the children in the park and playground,” said Jamal Bafadhal, 63, a neighbour. “From the outside to look at him you thought he was a good guy. But he was a little bit removed from us.”

Salahudee Jayabdeen, 40, said the man had been forcibly removed from a local mosque, Jabir bin Zayd.

“He started questioning what the imam was saying,” he said. “He was asked to leave. He didn’t want to and was forcibly taken out.”

A mosque spokesman confirmed the incident had happened, but said the man involved was not a regular and was not known to them.

The three attacks in Westminster, Manchester, and now London Bridge have claimed 33 lives in total, and constitute the worst wave of atrocities to hit the UK since the London suicide bombings on 7 July 2005. Five other plots believed to be at an advanced stage have been disrupted since the Westminster Bridge attack on 22 March – four in London and one in Birmingham.

Following a Cobra emergency committee meeting on Sunday, attended by police and security chiefs, the prime minister, Theresa May, said that while terrorists involved in the three attacks were “not connected by common networks”, a new threat was emerging of attackers who “are inspired to attack not only on the basis of carefully constructed plots after years of planning and training … but by copying one another”.

May announced a review of counter-terrorism legislation including the possibility of longer sentences for terror offences and a campaign against the “evil ideology of Islamist extremism”.

She said “enough is enough” and reiterated her call for international agreements to “regulate cyberspace”, accusing internet companies of creating a safe space in which extremist ideology could breed. Facebook, Google and Twitter all defended their record and said they wanted to work with government to prevent terrorists using their platforms.

“We want Facebook to be a hostile environment for terrorists,” said Simon Milner, director of policy at Facebook UK, Middle East and Africa.

The mayor of London, Sadiq Khan, announced that a vigil would be held next to City Hall, by Tower Bridge, on Monday evening from 6pm “to show the world that we stand united in the face of those who seek to harm us and our way of life”.

The Joint Terrorism Analysis Centre has left the UK terror threat level at severe, meaning an attack remains “highly likely”. It was raised to critical – the highest level – in the wake of the Manchester arena bombing and was returned to severe last Saturday.