The Information Commissioner's Office has announced it will contact 1,200 UK construction workers who may have been blacklisted because they were involved in union activities.

The move follows the discovery of a "secret" list, which includes names and index cards of 3,200 blacklisted workers and environmentalists.

The document, which was held by The Consulting Association, was uncovered by the ICO in 2009, but construction companies have denied legal liability.

The firms, however, said they would offer to pay up to £100,000 ($161,710, €120,105) to victims.

"We're asking those people to reply to us and provide some form of identification if they would like us to check whether the information included on the list is about them," said David Smith, deputy commissioner and director of data protection.

He added: "If it is, then they will receive a copy of their information. How much detail they'll receive in response to their enquiry will vary in each case."

The ICO said it has had trouble contacting potential victims because, even though some of the names listed have other details recorded alongside them, such as National Insurance numbers and dates of birth, some of the cards contain very little additional information and what they do contain is often out of date or inaccurate.

Earlier this year, the ICO wrote to 103 people in the cases where it had the individual's address and were able to establish its accuracy with the help of Equifax.

In total, the organisation has taken more than 4,000 calls from people wanting to know if their name was included on the blacklist.

The ICO also received more than 1,200 written requests, from which 467 individuals have been provided with copies of their information.

The announcement follows protests led by trade unions UCATT, Unite, GMB and the TUC to raise awareness of blacklisting.

Jerry Swain, regional secretary of construction union UCATT's London and South East Region, said: "Blacklisting is a disgusting and vile act which destroyed the lives of workers and their families.

"The companies involved in blacklisting must fully compensate their victims and there must be a public inquiry to discover the full truth about what occurred."

The day of action took place across the UK and outside of firms allegedly involved in blacklisting.

In addition, UCATT said it has commenced legal proceedings against many of the companies allegedly involved in the blacklisting.