Construction workers demanded answers from the Information Commissioner's Office today after it emerged that the public is in "complete ignorance" of the true extent of blacklisting in the industry.
The ICO seized a blacklist from the offices of the Consulting Association (CA) in a 2009 raid.
More than 3,200 names were on the blacklist, which boss Ian Kerr used to pass on details of trade union activity to over 40 major construction companies.
But ICO investigations manager David Clancy revealed to the Scottish affairs select commitee on Wednesday that only 5 per cent of CA's files had been taken in the swoop.
He said he was confident that the cache included the whole blacklist, but the committee could barely believe Mr Clancy's disclosure.
Committee chairman Ian Davidson said that the ICO's failure to examine all the material had left the public in "complete ignorance" and could mean that many workers remained unaware that they had been blacklisted.
"There could have been twice as many names, or 10 times as many names in there," he said.
"To use a police analogy - if they had found drugs, they might have gone on to find two handguns."
He said he was surprised the ICO stopped at that point saying he did not understand why it had not gone through all the other documentation to establish whether it was relevant.
The committee also criticised the fact that a large number of the 3,200 individuals on the database had still not been contacted by the ICO, three years after the raid.
Construction union Ucatt said that there could potentially have been up to 60,000 additional people who had been blacklisted.
General secretary Steve Murphy said: "This is scandalous. We are seeking an urgent meeting with the ICO so that they can explain their actions. We need to know why the ICO left 95 per cent of the files with a criminal and where those files are now."
The ICO had not responded to requests for comment by time of press.
nPickets from construction union Unite blocked rush hour traffic on Oxford Street on Wednesday evening to demand the reinstatement of 28 workers effectively sacked for raising safety concerns on the Crossrail project.
Crossrail halted the EIS contract three years early after its unionised workers pointed out problems.
Unite says senior directors of BFK - the firm building Crossrail - have proven links to the Consulting Association.
The union is asking people to protest by emailing the employers at email@example.com.
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