Almost 800 workers who were blacklisted by construction companies for their political views and union activities have won an estimated £75m in a wave of new settlements.

Under the deals 771 workers will each receive an average of £65,000 after the industry agreed to pay £50m in compensation as well as about £25m in legal fees.

Some of Britain’s best known building firms, including Carillion, Balfour Beatty, Costain, Kier, Laing O’Rourke and Sir Robert McAlpine were accused of blocking workers whose names appeared on a list held by a shadowy trade group based in the Midlands.

Unite the Union announced on Monday that it had reached a settlement with eight construction companies that will see 256 workers share more than £10m of compensation.

The GMB has also revealed that it settled for 116 blacklisted workers at a total of £5.4m plus £3m of legal costs in April – and can now divulge the terms of that arrangement.

Other settlements have also been obtained by the union UCATT and by a law firm called Guney, Clark and Ryan.

The industry had already set up a compensation scheme worth an estimated £10m three years ago but unions continued to fight for more generous payouts.

The unions also called for a public inquiry into what they describe as a shameful incident in industrial relations.

The existence of the blacklist was uncovered seven years ago by the Information Commissioner’s Office when it raided the Droitwich offices of the Consulting Association.

The list allegedly stretched to 3,213 named individuals with personal information — gathered over more than 15 years — including political views and union activities. In some case the paper files included details of personal relationships.

The colour coded files also included the details on nearly 200 environmentalists and animal rights campaigners.

The mainly paper database was used by the construction groups to vet recruits and share information across the industry. The aim was to identify suspected “trouble makers” taking part in trade union activity or raising health and safety concerns.

The industry has always claimed that the practice did not amount to “blacklisting”, which usually means automatic discrimination.

But it has accepted that its secret vetting system infringed workers’ rights to confidentiality, privacy and reputation.

“Unite is proud to have fought right to the end to get the maximum we believed was possible against companies that had to be dragged kicking and screaming to make unprecedented admissions of guilt last October,” said Howard Beckett, director of legal services at Unite.

“In addition to financial compensation, admissions of guilt and formal apologies, the companies have agreed, as a result of this litigation, to issue guidance to site managers to ensure blacklisting is not occurring on a local level.”

Dave Smith, secretary of the Blacklist Support Group, said the result was a “historic victory for the trade union movement” after years of denials and cover-ups.

Tim Roache, GMB general secretary, said the companies involved had thought that they were above the law: “Finally they have been held to account in public and at great cost to them financially and reputationally. Government and employers’ organisations must never forget this sordid episode.”