Employers were keen to keep their jobs trouble free and prevent known union activists from getting a start on site.
Information on construction workers was compiled by the Economic League which was formed in 1915 to protect the interests of big business.
The League held information on union activists and members of left-wing political parties until it was finally disbanded in 1993. Contractors paid fees to the League to check-out potential employees against their database.
Most of the information during the past 20 years has been held on M&E workers and steel erectors who are considered the most militant sector of the industry.ADVERTISEMENT
The operation of blacklists was common-knowledge throughout construction but finding proof of their existence has proved more difficult.
A former director of Balfour Beatty subsidiary Haden Young struck the first major blow against the practice back in 2005 when he published the names of 1,000 blacklisted electricians.
His claims came in an industrial tribunal case where he said names of вЂњknown troublemakersвЂќ from former jobs at the Jubilee Line Extension, the Royal Opera House and pharmaceutical giant Pfizer's research centre in Sandwich, Kent.
Further allegations were made by a national newspaper investigation last summer which prompted the latest Information CommissionerвЂ™s Office probe and the subsequent publication of 40 construction companies who used blacklists.
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