Scotland Yard has been accused of seeking to cover up its involvement in the blacklisting of more than 3,200 construction workers following the emergence of minutes of a meeting between a senior officer in its anti-extremism unit and the organisation running the list.

The leaked document proves that as late as 2008 a detective chief inspector in the National Extremism Tactical Coordination Unit (Netcu) briefed members of the Consulting Association, the secretive organisation that ran the blacklist keeping people out of work for decades. The association, which had a database of 3,213 names on which it held information, was raided and closed in 2009 by the Information Commissioner’s Office, but not before it destroyed the professional and personal lives of thousands of workers, according to those on the list.

A committee of MPs holding an inquiry into its activities heard evidence that at least two of those blacklisted committed suicide as a result. In 2012 the Information Commissioner’s Office told an employment tribunal that it believed information held in the files was from the police or security services.

But the police have refused to confirm any flow of information between police officers and the association, which over nearly four decades kept files on trade union activists and workers who highlighted health and safety failings. An admission by the Independent Police Complaints Commission last year that it was “likely that all special branches were involved in providing information” was later contradicted by a senior officer at Operation Herne, an inquiry examining the activities of undercover officers. Detective inspector Steve Craddock told victims’ lawyers the IPCC’s statement was incorrect and that he had seen “no conclusive evidence” that Scotland Yard shared information with the blacklisters.

The leak appears to offer compelling evidence of a flow of information between the police and the blacklisting operation. The two-page document contains minutes of a meeting between six representatives of construction companies, including Sir Robert McAlpine and Costain, with detective chief inspector Gordon Mills at the Bear Hotel, Woodstock, Oxfordshire.

Mills, now a lecturer at Anglia Ruskin University, was a “senior officer in national extremism unit dealing with UK domestic extremism”, according to his profile on the online networking site LinkedIn. It adds that during his time at Netcu he became experienced in assisting “in investigating serious crime associated with domestic extremists; and forging effective partnership working with major organisations”.

The document, written by Ian Kerr, who ran the association, is illegible in parts but appears to suggest that Mills was there to explain the tactics and structure of police efforts to fight domestic extremism. The notes say Mills told the group the unit was expanding and that the purpose of the meeting was “to liaise with industry”.

Labour MP John McDonnell, to whom the document was leaked, has written to home secretary Theresa May to demand an independent inquiry into blacklisting and the role of the police . He writes: “DCI Mills was head of Police Liaison at Netcu and it is alleged that his role was to provide information from the police to companies. Netcu was subsequently subsumed into the National Domestic Extremism Unit of the Metropolitan police, but despite numerous requests under the Freedom of Information Act for documents relating to Netcu’s activities, the response has been that no documents relating to the meeting of DCI Mills with the association exist. It appears odd that no report of such an important meeting was written and that no evidence of the meeting is now held by the Metropolitan police.”

Dave Smith, a campaigner for the victims and an engineer who had a 36-page file against his name and was victimised for highlighting safety hazards on sites, said: “We have been saying for five-and-a half years that the state was involved in blacklisting and we have been told time and time again that is not true and been accused of being paranoid. It is a cover-up. We have a name of a senior police officer, not a rogue constable, who was meeting with them. There must be documentation held by the police and correspondence between the police and the association.”

Sarah McSherry from Imran Khan and Partners, representing victims, said that her clients had serious concerns that the police were seeking to cover up their involvement. She said: “Even the least cynical of people might consider this exercise to be framed not by the complaint made but by the desired outcome of the police.”

Only one firm, Amec, responded to questions from the Observer. It claimed it stopped using the association in 2007.