The Information Commissioner's Office (ICO) has located and seized a secret database containing personal information on over 3,000 UK construction workers, used as a vetting tool by more than 40 construction companies.

The 15-year old database of 3,213 workers includes details such as employment history and personal relationships, trade union activity and political leanings.

"This is a serious breach of the Data Protection Act [DPA]. Not only was personal information held on individuals without their knowledge or consent, but the very existence of the database was repeatedly denied," said deputy information commissioner David Smith.

The database was uncovered during a raid by the ICO on a company called The Consulting Association, based in Droitwich, West Midlands, on 23 February 2009, following an article printed in The Guardian in June last year.

Evidence found at the site indicated that around 43 well-known construction companies paid an annual fee of £3,000 to The Consulting Association's owner, Ian Kerr, to access the database. Subscribers were allowed to add and update information on new and existing workers, and could obtain details on individuals listed in the system for a fee of £2.20.

"The covert system enabled Mr Kerr to unlawfully trade personal information on workers for many years, helping the construction industry to vet prospective employees," said Smith.

"On raiding Mr Kerr's business premises we discovered an extensive operation involving household names in the construction industry. Kerr held information on thousands of construction workers, and profited by checking names against his database."

The ICO has served an Enforcement Notice (PDF) instructing Kerr to stop using the system, and to cease trading by the end of the week. He now faces prosecution for breaching the DPA. The ICO confirmed that Kerr had ceased trading, and had vacated his business address.

"We will prosecute Mr Kerr, and we are also considering what regulatory action to take against construction firms who have been using the system," said Smith.

"I remind business leaders that they must take their obligations under the DPA seriously. Trading people's personal details in this way is unlawful, and we are determined to stamp out this type of activity."

The ICO also announced that it will open a dedicated enquiry system from 16 March for people who believe that personal information about them may be held on the database, and is asking people not to contact the ICO before that date.