Assistant commissioner Mark Rowley disclosed the figures as he launched a major appeal for the public to report any suspicions and act on their instincts, saying their help is critical to foiling atrocities.
The Metropolitan Police officer said that since June 2013, police and intelligence agencies have disrupted 13 terrorist attack plots. Information from members of the public has contributed to stopping some of those attacks, while figures show it has assisted counter-terrorism police in a third of the most high-risk investigations.
Describing the contribution as “extraordinary”, Mr Rowley said: “Some of that information is a change in someone’s behaviour, some of that’s about suspicious activity.
“Sometimes that public information has actually started an investigation. Other times it’s part way through and it corroborates some things or adds to things we already know.
“The public are making a great contribution which is critical to us all working together to protect ourselves from terrorism.”
Despite foiling a string of plots since the murder of Lee Rigby in May 2013, the senior officer stressed that the threat continues to be severe while authorities have some big operational challenges.
Investigators have been making arrests at a rate of close to one a day on average since 2014. The official threat level for international terrorism has stood at severe – meaning an attack is “highly likely” – for more than two years.
Mr Rowley said that “tempo” of activity continues. He identified a host of challenges including encrypted communication methods, propaganda and the range of possible attack methods.
“Now we worry about everything from fairly simple attacks with knives or using vehicles all the way through to the more complex firearms attacks,” he said.
“All of that means that our job remains difficult. We’ve got over 500 investigations at any one stage.”