The "Stop Terrorists' and extremists' Online Presence" (STOP) campaign focusses on a concerted 36-hour campaign to involve the public in the work of the Counter Terrorism Internet Referral Unit.
Police forces have been using their social media channels from today to urge the public to report material they suspect is extremist or terrorist in nature by clicking on a distinctive red STOP button that can be found on their websites.
This then leads to an anonymous form for them to provide the information to their local force.
This year the unit is on course to remove 100,000 items, having already taken down 26,000 pieces of internet content in the first quarter of this year.
Scotland Yard's deputy assistant commissioner Helen Ball, the senior national coordinator for counter terrorism policing, said: "The internet and social media provide many opportunities for those with extreme views to target young or vulnerable people and their methods are constantly evolving, from using new phone apps to hijacking popular hashtags in order to reach wide audiences.
