Mark Kennedy accuses senior officers of suppressing vital evidence

The undercover policeman at the centre of the storm over infiltration of the environmental protest movement today insisted that all his actions had been sanctioned by his superiors and accused senior officers of deliberately suppressing evidence that would have exonerated six activists facing criminal charges.

Mark Kennedy, whose seven-year career as an undercover officer in the protest movement was detailed by the Guardian last week, broke his silence in a newspaper interview in which he rejected claims he had acted as an agent provocateur by orchestrating and financing protests. He also said he knew of 15 other undercover officers who had infiltrated green protest groups in the past decade, and of four who remained undercover.

Kennedy told the Mail on Sunday he had been "hung out to dry" by his former employers. "They sanctioned every move I made. I did not sneeze without them knowing about it."

He also dismissed as a "smear campaign" claims that he had slept with activists in order to get information.

The most damaging revelation from Kennedy concerns the botched prosecution of six activists charged with conspiring to commit aggravated trespass over a protest at the Ratcliffe-on-Soar power station in Nottinghamshire in 2009.

Prosecutors unexpectedly abandoned their trial last week after the activists' lawyer asked for documents detailing Kennedy's role in organising and funding the planned protest.

On Friday, the Independent Police Complaints Commission launched an investigation into allegations that the Nottinghamshire force had withheld material from the CPS and the activists' defence team.

Yesterday, Kennedy revealed that he had covertly recorded two meetings of activists held to discuss the break-in of the power station. "The truth of the matter is that the tapes clearly show that the six defendants who were due to go on trial had not joined any conspiracy," he said. "The tapes I made meant that the police couldn't prove their case. I have no idea why the police withheld these tapes."

Last night Mike Schwarz, the lawyer from Bindmans who represents the activists, called for a full scale judicial inquiry into the case and the "wider concerns about the use of undercover police, particularly against those exercising democratic rights of protest and expression". Schwarz, who said the failure to disclose the recordings could have perpetrated a miscarriage of justice, is demanding copies of all covert recordings and reports sent by Kennedy to his handlers as they could also cast doubt on the convictions of 20 other activists who, in a separate trial last month, were found guilty of a conspiracy to commit aggravated trespass during the same protest. Those activists, however, had argued a different defence.

In his interview, Kennedy detailed how the recording of the first day of the activists' meeting did not work as his handlers had failed to charge the battery on the device. However on the second day, he recorded an activist called Spencer Cook telling more than 100 other campaigners what the planned protest was about.

Kennedy told the paper: "During that briefing, Spencer was very clear that this was a volunteer-only operation and it was down to the individual to decide what role they wanted to play.

"There was no pressure on anybody to take part in anything they didn't want to do. I just assumed that the police would naturally put my tapes into evidence. Clearly I was wrong."

At the trial which was abandoned before it started last Monday, the six activists were going to argue that they crucially had not decided to take part in any conspiracy to break into the power station before the police pre-emptively arrested them and 108 other activists at a school on the eve of the planned protest.

Danny Chivers, one of the six, said: "The police appear to have behaved completely disgracefully. They appear to have used false charges as a way of harassing and deterring people from taking political action".

Nottingham police and the National Public Order Intelligence Unit, the agency which ran Kennedy, could not be reached for comment yesterday.