Counter-terrorism units have been making arrests on a near daily basis amid a huge effort to contain the threat to the UK.
Activity by police and security services has been running at a high level for a number of years as they attempt to defend Britain against dangers ranging from lone wolf strikes to complex, mass-casualty plots.
Figures show there were 260 arrests for terrorism-related offences last year.
This was a slight fall compared to the previous year, but the number remained high compared with other recent years.
In March it was revealed authorities have thwarted 13 potential attacks in less than four years.
The official threat level for international terrorism has been at severe, indicating an attack is "highly likely", since 2014.
While Islamic State remains a major focus of the work of police and intelligence agencies, security officials have repeatedly stressed that the threat posed from al Qaida remains.
Counter-terrorism authorities are also handling a rising number of cases of far-right extremism.
Although the pace of activity has been constant, Thursday's operations stood out from the relatively constant stream of arrests in recent years for different reasons.
Firstly, because of the location of the swoop in which a man was held in Whitehall. He was arrested just yards from the scene of last month's deadly attack by Khalid Masood in Westminster.
Then in an unconnected operation armed officers launched a raid on an address in north London in which a woman was shot.
Although police conduct thousands of firearms operations every year, incidents in which officers discharge their weapons are extremely rare.
Met chief says London arrests have 'contained' imminent terror threat
Met deputy assistant commissioner Neil Basu said today that he believed police had 'contained' the threat from both the Willesden incident and the earlier terror arrest in Westminster.
Speaking outside Scotland Yard he said armed counter-terrorism officers using CS gas stormed a house in the Willesden area of the capital on Thursday evening which had been under surveillance, shooting a woman in her 20s
In a separate incident on Thursday, a man was arrested carrying knives near Prime Minister Theresa May's office in Westminster and he remains in police custody, Basu said.
His statement said: 'Yesterday was an extraordinary day in London so I wanted to update you on the two separate unconnected and ongoing counter terrorism investigations that happened in the last 24 hours.
'Given the horrors in London of a few short weeks ago - and our thoughts are still with the victims and survivors of that dreadful day
'I wanted to reassure the public that our increased activity to combat terrorism over the last two years continues - both by police and security services
'Activity continues around the clock to identify and stop these threats and we are making arrests on a near daily basis.
'I want to pay tribute to the bravery of my uniform and detective colleagues who are doing that work to keep us safe.
'So - to yesterday's events: In Whitehall, a 27-year-old man was arrested by armed officers from the Met's Specialist Firearms Command, who stopped and searched him as part of an ongoing counter terrorism investigation.
'He remains in our custody having been arrested for Terrorism Act Offences and possession of offensive weapons and there are two ongoing searches at addresses in London as part of that investigation.
'In our second and unrelated investigation, last night at just before 19:00hrs, our highly trained firearms officers carried out a specialist entry into an address in Harlesden Road that we had under observation as part of a current Counter Terrorism investigation.
'An armed entry was necessary due to the nature of the intelligence that we were dealing with, and involved armed officers firing CS into the address.
'During the course of that operation one of the subjects of that operation - a woman - was shot by police - she remains in hospital. Her condition is serious but stable. Because of her condition she has not yet been arrested. We are monitoring her condition closely.
'As is routine we have informed the Independent Police Complaints Commission.
'In total six people have now been arrested in connection with that investigation - five at or near the address and one in Kent.
'The two further arrests were made when a man and a woman - both aged 28 - returned to the address later last night.
'Searches are ongoing at three London addresses - including Harlesden Road - as part of this investigation.
'Due to these arrests that we have made, I believe that we have contained the threats that they posed.
'With the attack in Westminster on 22 March so fresh in people's minds, I would like to reassure everyone that across the country officers are working round the clock to identify those people who intend to commit acts of terror.
'After that attack, we increased the number of officers on duty patrolling at key locations - and that continues as we police against the backdrop of a severe terrorist threat.
'There are constant acts of immense bravery by officers - armed and unarmed - those that the public see when our officers run towards danger, just like yesterday, but a huge amount of unseen work that the public will never know about from us and our brilliant security services.
'I would also like to thank the public for their continued help and support. No matter how hard we try it is communities that will defeat terrorism and we rely on your vigilance.
Please continue to let us know of any suspicions or concerns you may have. No call is ever a waste of our time and every call is treated seriously and confidentially and investigated.
'We will continue to work with all communities to defeat terrorists together - we will not allow common criminals to spread discord and fear.
And lastly can I thank the public for their bravery and help; for remaining calm and tolerant and being a fantastic advert worldwide for democracy, diversity and freedom.'