Senior managers at Crossrail, the huge publicly funded rail project in London, hired a corporate security company to monitor trade unionists who were campaigning against blacklisting across the construction industry, previously secret documents reveal.

The managers paid £59,000 to the company, Control Risks, over three years. They said the monitoring of the trade unionists was part of work to protect the project from outside threats.

The project to build a 73-mile east-west rail line across London is funded by the Department for Transport and Transport for London (TfL), the capital’s public transport authority.

The documents show how the security company compiled weekly reports on the trade unionists who were seeking justice for blacklisted workers.

Control Risks tracked their campaign, analysing their tactics and the impact of their protests. It identified influential figures in the anti-blacklisting campaign and its potential future activity.

The trade unionists were supporting an electrician who said he had been blacklisted and sacked from the Crossrail project.

In 2009, a watchdog closed down a blacklist funded by the construction industry containing files on thousands of workers they deemed to be troublemakers. Trade unionists campaigned to get compensation for those who had been denied jobs for long periods.

Crossrail has denied using blacklisting on the project.

Managers have been criticised for spending money on monitoring the trade unionists when their project has run almost £3bn over budget and its opening has been heavily delayed.

The decision to hire Control Risks would have been authorised by Chris Sexton, the project’s technical director until last year, according to TfL. He has since been promoted to be its deputy chief executive.

The reports of the monitoring operation – codenamed Project Galahad – were sent to senior Crossrail executives. Control Risks was paid £47,857 in 2013 and £11,309 in 2010, according to TfL.

In a statement, Crossrail said Control Risks had been hired “as part of its security planning … to assess external threats to the project, including, for example, terrorist threats, criminal threats and threats from direct action.

“Control Risks identified information that was available publicly, analysed that information and produced reports on the information that was relevant to the Crossrail project.” This included information about allegations of blacklisting, it added.

Control Risks said it “gathered information solely by looking at social media, websites and news reports. No interviews or on-the-ground information gathering took place.” It said work helped “Crossrail meet its duty-of-care obligation towards its employees”.

Control Risks, founded in 1975, is one of the UK’s oldest private security companies. It styles itself as “a specialist global risk consultancy”, giving advice to large corporations, carrying out investigations and providing security to governments and security for companies. It is understood to recruit former spies and military personnel.

Some documents about the monitoring were obtained by Frank Morris, the electrician, under the Data Protection Act.

With the support of the trade unionists, Morris campaigned to get his job back at the Crossrail project after he said he had been blacklisted and dismissed for voicing safety concerns. His claim was rejected by Crossrail, which said Morris was among 28 workers made redundant when a section of work had been completed.

The documents obtained by Morris show Control Risks monitored him and other anti-blacklisting campaigners between May and September 2013, drawing on material on the internet.

One exchange of emails show Crossrail asking Control Risks how many protesters were going to demonstrate at a court hearing at which Morris was taking legal action.

Morris criticised the “mismanaged” Crossrail project for carrying out monitoring that was “wrong”. “Big business is spending large amounts of money to keep me under surveillance and deny me work,” he said. “It sounds like something from a Hollywood film but it’s actually the dirty hidden secret of much industrial relations in the UK today.”