Police are asking the public for more help in thwarting terror attacks after more than a fifth of calls to them yielded useful intelligence last year.
The Metropolitan Police's Assistant Commissioner Neil Basu said: "If you feel nervous about it, you should report it".
He added that police want every good citizen to become "a counter-terrorism citizen".
It comes as police launch their Action Counters Terrorism campaign.
The campaign - encouraging people to report suspicious behaviour - comes as figures reveal 30,984 reports were made to counter-terror officers in 2017.
More than 6,000 of those reports helped inform live investigations, police say.
Mr Basu added: "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."
The call for action from the public comes just before the first anniversary of the Westminster attack in 2017, which was one of five terror attacks which took place in the space of six months.
Figures show the police and MI5 are running more than 600 counter-terror investigations relating to about 3,000 individuals.
Examples of suspicious activity include receiving deliveries for unusual items bought online, travelling for long periods without being clear where, and taking photos of security measures or CCTV cameras.