An obscure unit within London's Metropolitan Police Service has been monitoring and keeping records on almost 9,000 political campaigners and activists using social media surveillance and other methods. A freedom of information request filed by the The Guardian reveals that the National Domestic Extremism Unit (NDEU) stores dossiers on 8,931 individuals labeled as "domestic extremists," many of which do not have any criminal record, according to a senior officer familiar with the unit's operations.

The NDEU has been monitoring the campaigners with a 24/7, 17-person social media surveillance team, which uses a technique called "Socmint" (Social Media Intelligence). The technique scrapes and analyzes Facebook profiles, Tweets, and other public data, using geolocation tracking and "sentiment analysis" tools to predict future crimes by determining targets' moods. The unit uses the strategy, along with undercover agents and paid informants, to monitor a wide range of individuals spanning the political spectrum, from the far-right English Defense League to animal rights advocates and anti-war protestors.

Regulations meant to prevent excessive police surveillance are in place under the UK's Regulatory Investigation Powers Act (RIPA), but the law, which passed in 2000, doesn't include any controls for police use of social media for investigations.

The documents come a day after it was reported that Metropolitan Police secretly eavesdropped on meetings between an attorney and the eyewitness of the 1993 hate crime murder of British teenager Stephen Lawrence. The eyewitness, Duwayne Brooks, had been targeted in a police smear campaign aimed at discrediting his testimony in the case, which finally ended last year with the conviction of two men after new evidence came to light.