The human rights group, Liberty, last week wrote to the Information Commissioner asking him to conduct a thorough investigation into 44 companies that were found to be blacklisting so-called “troublemakers” as long ago as 2009.

The extent of the problem became apparent following a raid by the Information Commissioners’ Office (ICO) in March 2009 on the premises of the Consulting Association.

ICO officials found a blacklist containing the names of more than 3,200 construction workers. More than 40 major construction companies - many of them household names such as Balfour Beatty, Sir Robert McAlpine and Carillion - were subscribers to the list.

The database was maintained by a man called Ian Kerr who carried out the day-to-day work of maintaining it and responding to employers’ requests for information about anyone involved in trade union activity, including raising genuine concerns about safety.

However, following the raid, the Commissioner took very limited action. Mr Kerr, who reportedly earned six figure sums for operating the list, was fined just £5,000 at Knutsford Crown Court for breaching the Data Protection Act and paid £1,187 costs.

Enforcement notices (requiring the unlawful activity to stop) were only issued against a handful of the companies who admitted being involved. The companies themselves were never separately investigated and most have got away scot-free.

Liberty says that the issue is of enormous public importance, arguing that contracting out the blacklisting of innocent workers, politicians and journalists is no better than farming out phone hacking to private detectives.

According to the organisation, most of the people on the list, which is also said to have included journalists and politicians, still have no idea that they were victimised in this way.

It now wants the Commissioner to take enforcement action where necessary and has warned that if it is unable to persuade him to discharge his public duty, it may have to seek the assistance of the courts.

Following the raid, the government carried out a consultation and amended the Employment Relations Act 1999 in March 2010 to outlaw the blacklisting of trade unionists.

Read Thompsons response to the 2009 raid

Read Thompsons response to the government consultation on blacklisting of trade unionists

To read the current Regulations, visit the government legislation website.

To read the government guidance on the draft regulations, visit the Department for Business Innovation & Skills website