The police or intelligence services have been accused of making data available on workers who might cause trouble so that construction companies would know not to recruit them.

The Information Commissioner’s Office (ICO) has said that the details of 3,200 people which the “clandestine” organisation the Consulting Association has on a database could only have come from the police or MI5. The organisation is said to be funded by big names in the construction sector and was set up originally as the Economic League, checking on Irish construction workers when the IRA was at its peak.

David Clancy, investigations manager at the ICO, said at an employment tribunal: “There is information on the Consulting Association files that I believe could only be supplied by the police or the security services.”

And he later told the Observer newspaper: “The information was so specific and it contained in effect operational information that wouldn’t have formed anything other than a police record.”

Labour MP John McDonnell said: “I am outraged at the systematic abuse of people’s rights. This has destroyed people’s lives, broken up families, ensured that people have not been able to earn a living. It has devastated people year after year, and nobody has listened to us. No one has been willing to believe the extent to which there has been collusion between police, security services and companies. It is all about the ability of companies to exploit workers and destroy anybody who stands up against them.”