Workers blacklisted by the construction industry over more than three decades have launched a high court claim against an industry giant for conspiring with other firms to keep them out of work.

The workers allege that the company, which also worked on widening the M1 motorway, was involved in an unlawful conspiracy to amass a database of information against thousands of people, which was used to prevent them earning a living in their trade.

The claim involves 86 of 3,400 workers in the files of the Consulting Association, a covert organisation paid by big names in the industry to collect damaging information on workers regarded as leftwing or troublesome. The files included information about trade union membership, relationships, friendships and political views, along with surveillance intelligence.

The value of the initial claim for loss of earnings and damages is estimated to be around £17m, but many more of the victims are expected to add their names to the action in the coming months, raising the potential claim against the construction industry to about £600m, according to one source.