Undercover Pc Mark Kennedy ‘really sorry for betrayal’

But in April 2009, when 114 people had gathered for a meeting at the Iona School in Nottingham, hundreds of police swooped on the building and arrested them all for “conspiracy to commit aggravated trespass”.

Ratcliffe-on-Soar was one of many actions in Britain and across Europe which Mr Kennedy was involved in, including the protests against the G8 summit at Gleneagles in 2005 which helped give birth to the Climate Camp movement.

When confronted, Mr Kennedy told the activists he left the police after the Nottingham arrests in 2009.

It is unclear whether this is true, or where he is now.

David Winnick, a Labour member of the House of Commons Home Affairs Select Committee, has called for Home Secretary Theresa May to make a statement to MPs on the case, saying his concern was “the manner in which it has been alleged that Kennedy acted almost as an agent provocateur”.

Former Met deputy commissioner Bob Quick told the BBC’s Today programme that the use of undercover officers was “an established tactic” for the police.

“There are some risks attached, and occasionally things do go wrong,” he said.

“Undercover officers are uniquely vulnerable individuals. Whilst they are, in my experience over 30 years, very dedicated, brave and very professional, they are vulnerable because they are being constantly exposed to potentially corrupting and criminal influences and all sorts of relationships they get into to try and become effective in securing intelligence about criminality.”

But he said it was “extremely rare” for undercover officers to change their position and begin to sympathise with the groups they had infiltrated.