Eight high-profile contractors made an ‘amended defence’ of their role in blacklisting at a High Court hearing in London this week.

The contractors involved are Balfour Beatty, Carillion, Costain, Kier, Laing O’Rourke, Sir Robert McAlpine, Skanska and Vinci.

A statement released by the eight companies said they had submitted an “amended defence” to the court on Wednesday in which they laid out a number admissions for their part in the blacklisting of workers.

The companies’ defence included “a full and unreserved apology” for their part in the “vetting of construction workers through the Economic League and The Consulting Association”.

The statement added: “We recognise and regret the impact it had on employment opportunities for those workers affected and for any distress and anxiety it caused to them and their families.”

Blacklisting came to light when in 2009 the Information Commissioner’s Office (ICO) seized a Consulting Association database of 3,213 construction workers and environmental activists used by 44 companies to vet new recruits and keep out of employment trade union and health and safety activists.

Talks between unions and the employers on a compensation scheme for workers broke down in June 2014 over the amount of money being put into the scheme by the employers.

The GMB union said the admission is a firm basis to make sure workers are given “very substantial compensation”.

Maria Ludkin, GMB national officer for legal and corporate affairs, said: “The fact that the companies have acknowledged the distress and anxiety caused to workers and their families now gives us a firm basis to make sure members are given the very substantial compensation they deserve, and that the true nature of the secretive Consulting Association is known.

“Even though it has taken years of fighting in the High Court, the companies have now acknowledged that they infringed workers’ rights to confidentiality, privacy, reputation and data protection, which is an important battle to have won.

“The next fight is to ensure the companies are properly held accountable so that this cannot happen again.”

Michael Newman of the law firm Leigh Day, which represents GMB members in the legal action against the construction companies, said: “Blacklisting is a timely reminder of the importance of trade union rights against the collective weight of corporate interests, and both the trade unions and the Blacklist Support Group have been tireless in their campaigning.

“For years the blacklisting construction companies have denied all liability, so these admissions represent a significant step towards securing the compensation these workers are due, and due recognition of the impact blacklisting had on their lives.”

Unite assistant general secretary, Gail Cartmail, said: “Blacklisting is a scandal that has ruined lives and led to hardship and misery for thousands of people. The admissions from the blacklisters and the damages for the blacklisted are an important step on the road to justice in righting that wrong.

“That road won’t be completed, though, or the stain of blacklisting removed until there is a full public inquiry and the livelihoods of the blacklisted restored by the firms involved giving them a permanent job.”

The building workers’ union UCATT said most companies involved in the blacklisting saga had admitted their liability, describing it as a “massive breakthrough”.

Its acting general secretary, Brian Rye, said: “This is a highly significant step forward in the battle for blacklisting justice. Finally the companies have admitted their guilt and have begun to apologise. However, we will continue fighting until justice is achieved for all our affected members.

“While the admission of guilt, and the apology to those who were blacklisted, is a massive step forward, the high court case will continue as the companies still will not accept the significant loss of earnings that the victims of blacklisting suffered.”