The Guardian claims police officers tried to spy on students at Cambridge University.
Footage obtained by the newspaper appears to show an officer trying to persuade an activist to become an informant in return for money.
The officer asks for information on potential supporters of groups including UK Uncut, the English Defence League, Unite Against Fascism and anti-fracking demonstrators.
He requested names of students going to protests and lists of the vehicles they were using.
But the would-be informant was secretly filming the meeting to expose what was going on.
Cambridge University declined to comment, saying it's a police matter.
A spokesman for the county's police force said:
"Officers use covert tactics to gather intelligence, in accordance with the law, to assist in the prevention and detection of criminal activity."
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