With 25 Islamist plots foiled in the last five years and four extreme right plots stopped since March 2017, the Home Secretary Sajid Javid this week described a "step change" in the terrorist threat to the UK. As a result, MI5 is to declassify and share information on UK citizens suspected of having terrorist sympathies. "Key" biographical data on - potentially - hundreds of people will be given to neighbourhood police, councils and other public agencies such as the Probation Service and the Charity Commission. Is this an example of sensible information-sharing in the interest of national security, or is it the problematic extension of counter-terrorism responsibilities to those who may not be qualified to handle them? Many believe that as the nature of terrorism is changing, so should our behaviour. Anyone can buy a knife and hire a van, therefore we - citizens, employees, officials - should all be vigilant and prepared to report our suspicions. But is all this suspicion good for us or can it result in an unhealthy culture of paranoia and vigilantism? The question goes much wider than terrorism. For example, should clergy, therapists, journalists and teachers be duty bound to report suspicions of criminality? Is respect for confidentiality no longer an unassailable virtue? Witnesses are Phillip Blond, Silkie Carlo, Adrian Hilton and Hannah Stuart.

Producer: Dan Tierney.