Some of Britain’s best known construction firms co-operated with a secret “blacklist” which stopped thousands of workers from getting jobs, a court has heard.

More than 40 firms were involved in a database of 3,213 construction workers which had been compiled by a Worcestershire firm and used to vet potential employees.

It emerged as Ian Kerr, who administered the list on behalf of The Consulting Association - described in court as a construction trade association - was fined £5,000 for a breach of the Data Protection Act.

Knowledge of the blacklist emerged in March when the offices of the Consulting Association, in High Street, Droitwich, were raided by the Information Commissioner’s Office (ICO).

Kerr, 66, of Avoncroft Road, Stoke Heath, Worcestershire, had pleaded guilty to a breach of the Data Protection Act in May.

He was fined £5,000 and ordered to pay the ICO’s costs of £1,187.

Angry former construction workers, sitting in the public gallery, jeered Kerr as the sentence was passed. Later, as he left court with his wife, the path of his car was blocked by the workers.

After the hearing the ICO said its investigation will continue to see if the construction firms had broken the law.

ICO investigator Dave Clancy said he was “satisfied” with Kerr’s fine and added that he hoped it would send a strong message to other organisations which operate such blacklists.

John Wyn Williams, prosecuting for the ICO, told the hearing at Knutsford Crown Court: “The Consulting Association was funded by a number of leading construction companies throughout the country.

“It would collate and provide information to construction companies in relation to individuals seeking employment in that industry.”

Mr Wyn Williams said the database included names, dates of birth and national insurance numbers.

He added: “Interestingly, it also included conduct which may impact on an individual’s chances for further employment.

“This information was to be used covertly. Individuals on the database were not aware of it and could not challenge the accuracy of the information.

“Over 40 subscriber companies from the construction industry used Mr Kerr’s service.”

The ICO says it believes Kerr ran the blacklist for up to 15 years.

It has named around 40 companies which were subscribers to the database, including Amec Construction, Balfour Beatty and Morgan Est.

Mr Wyn Williams said the Association’s accounts showed that between 2004 and March 2009, when it ceased trading, around £478,000 was paid to the organisation by various firms.

Jamie Strong, defending, said Kerr was one of four employees of the Consulting Association earning £48,000 a year at the time of the ICO raid.

He said most of the information on the blacklist was provided by the construction firms to share with other companies in the industry.

He described Kerr as the “central point of contact” and said: “Mr Kerr facilitated the exchange of information.”

Judge Stephen Clarke said: “The nature of the list was to provide to major construction companies a list of people effectively for them to avoid employing.

“The list may or may not have been accurate. There was no way for you to find out if you were on such a list.”

The judge added: “You would hope that this register will not continue in another guise.”

Mike Abbott, 77, from Wigan, Greater Manchester, was named on the blacklist in the late 1970s.

He said during a five year period he was only offered two jobs until 1983 when he left the industry and started his own business.

He said: “I couldn’t feed my children because of that list and all Kerr gets is a £5,000 fine. I am very angry about what he did to me and many others. But he was just a front for all this.

“Those who are really responsible should now be prosecuted.”

David Smith, deputy information commissioner, said: “Ian Kerr colluded with construction firms for many years flouting the Data Protection Act and ignoring people’s privacy rights.

“Trading personal details in this way is unlawful and we are determined to stamp out this type of activity.”

The ICO said it has received around 1,827 enquiries from members of the public and as a result more than 120 individuals who appeared on the database have now had their information returned to them.