Fifteen minutes into Lucy Parker’s film, Solidarity, what looks like some kind of rooftop reunion barbecue between long-term former colleagues takes a more serious turn. There is talk of family breakdowns and even suicide after those gathered lost their jobs and struggled to find another one. This was largely down to their names appearing in reports compiled by a body called the Consulting Association, which pointed out various reasons why they shouldn’t be employed.

It’s a moving moment in Parker’s film, which receives its Scottish premiere in Stirling next week as part of the Central Scotland Documentary Festival. A Glasgow screening follows later this month care of Document Human Rights Film Festival. The moment is given extra poignancy by the fact that those gathered on the roof are victims of blacklisting, who have gathered to share experiences of having their livelihoods, relationships and in some cases their entire lives destroyed.

These scenes are part of a remarkable picture built up by Parker in her 75-minute opus, which calmly moves between the rooftop meeting, a public meeting highlighting state infiltration of protest groups, reconstructed court hearings relating to the blacklist by law students and archive footage of Westminster’s 2013 Scottish Affairs Select Committee Inquiry into the Consulting Association, in which the organisation's key players are cross-examined by MPs led by Labour’s Ian Davidson.

“I didn’t imagine making a film like this at the start of the process,” says Parker, a former film-maker in residence at Berwick Film and Media Arts Festival, who has been working with producer City Projects for 5 years to make the film. “The subject matter of the film, the legal processes I witnessed and the people I met shaped the creative decisions I made. One thing I didn’t want the film to do is put people off joining a trade union because of the fear of blacklisting. Through the film I wanted to show the solidarity that the movement offers workers.

“I also wanted to show how blacklisting wasn’t just a case of certain individuals making rogue decisions, but that state involvement has been revealed through links to undercover policing. There are so many layers, as I was making the film more information was being made public, it was difficult to know when to stop filming.”

Presented without any kind of narration, Solidarity’s jigsaw-like construction evolves into a devastating indictment of the Consulting Association. Operating between 1993 and 2009, this bland-sounding organisation was formed from the ashes of the equally grey Economic League. That body had previously held files, not just on construction workers, but on politicians including former Prime Minister Gordon Brown before being wound up following a parliamentary inquiry into its activities.

The Consulting Association’s demise was more dramatic. A raid on its offices in the Worcestershire spa town of Droitwich by the Information Commissioner’s Office seized 3,213 files on construction workers seen as trouble-makers of one form or another, often relating to trade union activity.

Companies using the Consulting Association included Sir Robert McAlpine Ltd, Balfour Beatty, Laing O’Rourke and other names familiar from the crowded Scottish skyline of construction sites. Developments in Scotland where workers were vetted by the Consulting Association include the Quarter Mile project in Edinburgh and the Marie Curie Centre in Glasgow.

Parker began work on Solidarity after meeting George Fuller, a blacklistee who appears in the film, while working on another project.

“I met George at a writing group he is a member of and learnt about his experience of being blacklisted for organising a petition around homelessness.” says Parker, “I then started going to the court hearings which was fascinating, but very difficult to follow, and I was determined to get my head round it. It made me think about how your work life and political life can be quite divided, and about what you can or can’t say.”

To this end, Parker’s film includes material relating to the infiltration of protest groups by undercover police. Two of the women, ‘Andrea’ and ‘Alison’ who were deceived into relationships with undercover police speak in the film about how they were used to infiltrate political groups and trade unions.

As Parker describes it, “It’s a really messy web.”

Solidarity premiered at Sheffield Doc/Fest earlier this year. This follows a work in progress shown at Rhubaba gallery in Edinburgh in 2015 as an art installation that also featured documentation of research materials. This included some of the Consulting Association’s actual reports on blacklistees, which read as Kafkaesque proof of how the establishment waged quiet war on their employees, who they presumed to be powerless.

The blacklistees, however, thought otherwise, and, the Blacklist Support Group, founded in 2009, have fought tirelessly for justice. While more than £20 million compensation has been paid out to blacklisted workers by eight companies, legal actions remain ongoing, as does a call for a full public inquiry into the blacklisting scandal.

With Solidarity’s quietly forensic eye making the film as much a work of art as a vital documentary study of social history in progress, Parker hopes to screen Solidarity at the Scottish Parliament in Holyrood at some point, with other potential Edinburgh screenings pending.

“Where the film ends, there’s a feeling of perseverance,” she says, “and a sense that those who were impacted will keep on working for justice, no matter what. That’s what I wanted to capture.”

Solidarity screens at Macrobert Arts Centre, Stirling as part of Central Scotland Documentary Festival on October 11 at 8.15pm, then at the CCA, Glasgow as part of Document Human Rights Film Festival on October 25.