As part of the ongoing 'ACT - Action Counters Terrorism' campaign, UK Counter Terrorism Policing is calling on the public to report any suspicious online content or activity.
This comes as the UK's specialist unit that deals with online terrorist material revealed that as well as taking down over 300,000 pieces of terrorist material, the unit has also provided key evidence and information in 226 counter terrorism investigations since it was established in 2010.
Commander Clarke Jarrett, head of the Counter Terrorism Command, said: "It's vital that if the public see something online they think could be terrorist-related that they ACT and flag it up to us.
"Our Counter Terrorist Internet Referral Unit (CTIRU) has specialist officers who not only take action to get content removed, but also, increasingly, are in a position to look at those behind online content - which is leading to more and more investigations."
Online terrorist-related material can be reported via http://gov.uk/act
In 2010, the UK established the world's first ever Counter Terrorism Internet Referral Unit (CTIRU), hosted within the Met's Counter Terrorism Command, to tackle the rise in terrorist-related material that was appearing on the Internet.
Since the CTIRU's launch, just over 304,000 pieces of terrorist-related material have been removed from the Internet. The majority of this content relates to Islamist extremism, but the unit has also seen an increase over the past year in content related to extreme right-wing ideology.
Around a quarter (481 = 26%) of all public referrals (1849) into the unit since March 2017 related to extreme right-wing material, although the vast majority of public referrals still relate to Islamist extremism.
In previous years the CTIRU has been focused on getting terrorist content removed from the Internet. But as their work and relationship with internet providers has developed to a point where more and more of the material is being removed automatically by the content providers themselves, the unit has been able to shift focus towards investigations.
As a result, over 226 counter-terrorism investigations across the UK have been supported or been provided with key evidence and information from the CTIRU.
In February, a man was jailed for encouraging terrorism and supporting a proscribed organisation as a direct result of a public referral that came into the CTIRU. A suspicious message had been sent to somebody living outside the UK, who then contacted UK authorities in March 2017 to alert them to the message.
The CTIRU made further enquiries and established the message was from a man - Mohammed Kamal Hussain, 28 (11.05.89) - from east London. They identified that Hussain had posted a number of messages on Facebook which glorified the violent activities of the terrorist organisation Daesh.
A fast-time investigation was launched by the Met Police Counter Terrorism Command who arrested Hussain on 30 June 2017, and he was subsequently convicted and jailed in February.
Commander Jarrett said: "This example shows how the public has a vital role to play in the fight against terrorism.
"I would urge anyone who comes across what they think could be extremist or terrorist material - whether it's right wing, Islamist or indeed any other form of extremism - to report it to us. Our specialist officers can then assess the material and take appropriate action to potentially prevent further terrorist activity from happening."