The counter terror police have launched a video campaign calling on the public to help the authorities.
The 60-second film shows a series of scenarios, such as a man stockpiling hazardous material and another buying weapons, before rewinding and zooming in on the danger.
An on-screen message reads: “Unfortunately life has no rewind button. If it doesn’t feel right, ACT.”
It will be shown at 120 cinemas across the UK over eight weeks from January 25.