Police are continuing to quiz seven people, including a suspected knifeman arrested in Westminster, held after separate counter-terror operations within hours of each other.
The swoops on a man, 27, in Whitehall and locations in north London and Kent were executed to contain threats of an "active" terror plot, Scotland Yard said.
One suspect, named as Khalid Mohamed Omar Ali, was arrested on suspicion of offences under the Terrorism Act and possession of offensive weapons close to Downing Street on Thursday afternoon.
Police recovered several knives during the "intelligence-led" swoop, which took place yards from the scene of last month's deadly attack by Khalid Masood on Westminster Bridge.
Believed to be a British national born overseas who went to school in Tottenham, north London, Ali reportedly joined a humanitarian mission to Gaza in 2010.
Following his dramatic arrest in front of large crowds of tourists, he was taken for questioning at a south London police station where he remains.
A further six people, including a 16-year-old boy, are in custody after they were detained in an unconnected operation that saw a team of specialist firearms officers storm an address in Willesden, north London.
They were all arrested on suspicion of the commission, preparation and instigation of terrorist acts and taken to a south London police station for questioning.
One has been named in reports as Mohamed Amoudi, 21, a Yemeni-born British citizen who studied physics at Queen Mary University in east London.
A woman in her 20s who was shot during the raid is being held under police guard in hospital, where her condition was described as serious but stable.
She is expected to be arrested when her condition improves.
Elite armed officers carried out a "specialist entry" into a terraced property in Harlesden Road shortly before 7pm on Thursday night.
Police fired CS gas into the address, which had been under observation as part of a current counter-terrorism operation.
Neighbours recalled hearing "at least six" shots and screaming as police entered the address.
Ruth Haile, who lives in the road, said she later saw an injured woman being treated and shouting: "Don't touch me, my body, don't touch my dress."
Alexandra Sabanov, a mother-of-one who lived next door to the raided house, saw "snipers" and officers wearing gas masks.
"We heard 'bang, bang, bang, bang', went to the window and just saw a number of armed police just there with their guns pointing at our next-door neighbour's window," she said.
Ms Sabanov said her neighbours were a "standard Muslim couple" of whom she "never suspected anything at all".
Giving an update on the two operations, Metropolitan Police Deputy Assistant Commissioner Neil Basu said on Friday: "Due to these arrests that have been made yesterday, in both cases I believe that we have contained the threats that they posed."
Mr Basu said an armed entry was necessary in Willesden "due to the nature of the intelligence that we were dealing with".
The Independent Police Complaints Commission (IPCC) has been informed of the incident.
Two of the arrests were made when a man and a woman, both aged 28, returned to the address later that night, Mr Basu said. Searches were also carried out at three London addresses.
Mr Basu said he wanted to reassure the public that officers were working around the clock to identify would-be terrorists.
Home Secretary Amber Rudd praised police and security services, adding that the public's role is "crucial in identifying suspicious activity" and urged anyone with concerns to contact authorities.
The official threat level for international terrorism currently stands at severe, indicating that an attack is "highly likely".
It was revealed last month that security services have thwarted 13 potential attacks in less than four years.
Meanwhile in a separate raid on Friday, a 47-year-old woman was arrested at an east London address on suspicion of conspiring to fund and support terrorism.
She was taken for questioning at a south London police station as part of an "ongoing investigation into the funding of terrorism in Syria", the Met said.
The arrest was not linked to Thursday's counter-terrorism arrests in London and inquiries are ongoing.