Police want members of the public to act as "counter-terrorism citizens" to help them stop deadly attack plots.
Security chiefs say information from the community is crucial to confronting the unprecedented threat - with more than 6,000 tip-offs yielding useful intelligence last year.
Launching a fresh drive to encourage reporting of suspicious behaviour or activity, Britain's new counter-terror police chief urged people to trust their instincts.
In one of his first interviews since his appointment, Metropolitan Police Assistant Commissioner Neil Basu told the Press Association: "There's no such thing as good training for this.
"It's about instincts and knowing your community. If you feel nervous about it, you should report it.
"It's long been a mantra in counter-terrorism policing that we want every good police officer to be a counter-terrorism officer.
"This is an opportunity for every good citizen to be a counter-terrorism citizen."
New figures show that 30,984 reports were made to counter-terror police online or over the phone in 2017.
Of those 6,659 - more than a fifth (21.5%) - resulted in information used by officers to inform live investigations or help build an intelligence picture of an individual or group.
On Tuesday police will release a new film and more detailed guidance on the types of behaviour they want the population to look out for as they launch the latest phase of the Action Counters Terrorism campaign.
Examples of suspicious activity could include hiring large vehicles or buying a large amount of chemicals, fertilisers or gas cylinders for no obvious reason.
Receiving deliveries of unusual items, looking at extremist material online, taking photos of security arrangements or going travelling for long periods without specifying the destination, could also be noteworthy.
Mr Basu said: "This is the planning cycle. Terrorists have to plan, they have to buy things.
"When they do these things they will look nervous, they will look out of place.
"We are looking for the public to pick up on signs like that and report to us."
Polling indicates that more than 80% of people are motivated to report suspicious activity or behaviour.
Mr Basu said: "The few people who don't want to report either don't trust us - let's be frank - or they think they are going to waste our time.
"What I would say is nobody is wasting our time. What you might have is an absolutely vital piece of that jigsaw that puts the whole investigation together.
"You don't need to worry about reporting to us.
"We will treat it appropriately, we'll treat it confidentially and with great seriousness. So please just have the confidence to pick up the phone or click on the mouse."
Since the start of last year police have foiled 10 Islamist and four right-wing terror plots.
Thursday marks a year since the Westminster atrocity - the first of five attacks that took place in less than six months.
Police and MI5 are running more than 600 live counter-terror investigations relating to 3,000 individuals.
There is also a wider pool of 20,000 former "subjects of interest" who have previously featured in probes and who are kept under review.
Mr Basu said: "2017 came as a shock to everyone but we've actually talked about the fact attacks will get through. This isn't a zero sum game.
"The public should feel reassured they can play a part in this but they've also got a global leading counter-terrorism machine that's working on their behalf."
Security minister Ben Wallace said: "The threat we face requires a response from all areas of society and I commend the public for their diligence in helping the police. Taking action can help save lives."
-Suspicious activity or behaviour can be reported by calling 0800 789 321 or visiting www.gov.uk/ACT