BLACKLISTED workers will demand compensation in court this week from eight construction firms for loss of earnings over decades.

More than 700 people in the construction industry represented by unions Ucatt, GMB and Unite have sued the companies for using a secret and illegal database for about 50 years to block those who reported breaches in health and safety from getting work.

The firms to stand as High Court defendants on Thursday are Sir Robert McAlpine Ltd, Balfour Beatty, Carillion, Costain, Skanska, Kier, Vinci and Laing O’Rourke.

They admitted in October that they broke the law by subscribing to the Consulting Association (CA), an organisation which maintained a list of trade unionists — effectively stopping them getting work — and by infringing rights of confidentiality, privacy, reputation and data protection.

Unions have already won £5.6 million in compensation for some victims, but othercases are being taken through the courts after a new blacklist of 3,213 workers was discovered.

A computer used by the CA that was “lost” for seven years was found by investigative journalist Phil Chamberlain in the home of former CA bookkeeper Mary Kerr, who is set to give evidence as a witness at the High Court.

The computer was seized during a raid on the Information Commissioners’ Office (ICO) in 2009 but was returned unexplored to CA chief executive Ian Kerr, Ms Kerr’s husband, who died in 2012.

The ICO did not even switch it on to analyse its data, the Blacklist Support Group said.

Commons committee MPs investigating the victimisation of unionised construction workers slammed the ICO for its lack of action.

“The CA and the construction industry went to great lengths to keep their operation secret,” said Mr Chamberlain.

Unite has won a defamation claim which means that the workers can demand full disclosure even if they settle with bosses.

“These defendants openly admit to the destruction of documents,” said Unite legal director Howard Beckett.

“Their attempts to deny meaningful levels of compensation and to deny conspiracy allegations rely upon the lack of records.

“This discovery allows the victims’ legal teams to further explore the possibility that undisclosed documents still exist, showing the true extent of those involved in the disgraceful practice of blacklisting.”