Several terror plots that "were very close to an attack" were thwarted "within minutes" of being carried out, London's most senior police officer has said.
Met Police Commissioner Cressida Dick told LBC that five terror attacks had been prevented in the last few months.
Four terror attacks have taken place in the UK in 2017 - three in the capital.
Ms Dick, who took charge of the Met in February, said the attacks in London and Manchester had been "horrific".
She said a "very large number of plots" have been foiled over the last few years.
Ms Dick said she could not reveal details about the nature of the terror plots because arrests had been made, but added: "We've had a huge number of successful operations.
"It's well into the teens in the past couple of years, where we know people were intent on attacking and that's been stopped."
She added: "In addition, [police have made] hundreds and hundreds of arrests of people who are radicalised and are either spreading hatred or supporting terrorism and wanting to carry out a terror attack."
Ms Dick, who was previously the police's lead on counter-terrorism, praised officers for their response to the attacks.
"At London Bridge it was utterly astonishing," she said.
The attackers - who killed eight people on London Bridge and in nearby Borough Market - were shot dead by armed police within eight minutes of the first emergency call.
UK terror attacks
- Westminster Bridge on 22 March: Six people died, including the attacker, and at least 50 were injured when Khalid Masood drove a car into pedestrians and stabbed a policeman
- Manchester Arena on 22 May: Bomber Salman Abedi killed 22 people and injured 116 in a suicide attack at an Ariana Grande concert
- London Bridge on 3 June: Eight people were killed when three men drove a van into pedestrians on the bridge and launched a knife attack in nearby Borough Market
- Finsbury Park on 19 June: A van drove into a group of worshippers close to a north London mosque, where one person - who had been taken ill before the attack - died and nine were taken to hospital
Ms Dick, who has called for more funding in the wake of recent attacks, said police officers relied on information from local communities to identify terror suspects.
"We clearly need a lot more [information] because what has happened in the last few months alone is horrific," she said.
"We are undoubtedly seeking examples of people who have carried out attacks or people who are violent extremists," she added.
"Essentially they're living in our communities and that's a problem for all of us."