This is as good an answer as any
Photographs, names and video footage of people attending protests are routinely obtained by surveillance units and stored on an "intelligence system". The Metropolitan police, which has pioneered surveillance at demonstrations and advises other forces on the tactic, stores details of protesters on Crimint, the general database used daily by all police staff to catalogue criminal intelligence. It lists campaigners by name, allowing police to search which demonstrations or political meetings individuals have attended.
Disclosures through the Freedom of Information Act, court testimony, an interview with a senior Met officer and police surveillance footage obtained by the Guardian have established that private information about activists gathered through surveillance is being stored without the knowledge of the people monitored.
Police surveillance teams are also targeting journalists who cover demonstrations, and are believed to have monitored members of the press during at least eight protests over the last year.