Excerpts from the 'secret recordings' - courtesy the Guardian
Police are using hundreds of paid informants inside protest groups to "feed them intelligence", according to evidence handed to the Guardian.
The paper says it has obtained tapes of discussions between men claiming to be undercover officers from Strathclyde Police and a Plane Stupid activist.
The recordings appear to show money being offered for information.
Strathclyde Police said officers had spoken to the group and the force had a responsibility to gather evidence.
The Guardian says the recordings were made during meetings between Strathclyde Police and Matilda Gifford, an activist with environmental protest group Plane Stupid, which campaigns against airport expansion.
The taped evidence appears to show her being offered money to reveal information about the organisation's members and tactics.
An indication was given that tens of thousands of pounds had been paid to other informers in the past. Miss Gifford's student loans were also discussed.
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In the three hours of recordings, the unnamed men also claimed to have a network of hundreds of informants inside protest organisations across the political spectrum.
The Assistant Chief Constable of Strathclyde Police, George Hamilton, told the Guardian the force had "a responsibility to gather intelligence".
"Officers from Strathclyde Police have been in contact with a number of protesters who were involved with the Plane Stupid protests including Aberdeen airport," he said.
"The purpose of this contact has been to ensure that any future protest activity is carried out within the law and in a manner which respects the rights of all concerned."
But Miss Gifford said police were trying to disrupt the legitimate activity of environmental groups.
She told the BBC that while payment was discussed, definite sums of money were never finalised.
"They never said an actual amount to me," she said.
"They wanted to discuss a business proposal in our next meeting, is what they said, so we never actually put a figure on it.
"They hinted it would be useful in terms of student loans."
Miss Gifford also said that Plane Stupid's lawyers had attempted to identify the officers involved, but without success.
Former Flying Squad chief John O'Connor described the matter as a "storm in a teacup" and that similar contacts are often made with individuals in protest groups and in the criminal world.
He told the BBC: "That's what the police do. The police don't sit in their ivory towers, and expect the phone to ring and be given intelligence information.
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