Media playback is unsupported on your device Media caption The Millennium Dome was built by workers who had been checked against a blacklist

The union Unite says it has evidence that the vetting of individuals by name in the building industry is still happening, four years after the discovery of a secret list that denied people work for years.

BBC Panorama reporter Richard Bilton has the first TV interview with the woman who helped run that blacklisting operation.

Howard Nolan did not know he was on the list. As an electrician he spent years working on Britain's biggest building projects, but then the jobs dried up and all he had were his suspicions.

"I always had continuous work and then, all of a sudden, nothing," he said.

Dark secret

In fact, he was one of the 3,200 men and women held on a secret and unlawful list of workers.

For almost two decades it was the UK construction industry's dark secret. Information was being collected about ordinary workers and fed into a blacklist. The workers did not know they were on the list but, once added, their life could be changed forever.

Publicly-financed construction projects such as the Olympic Park, the Millennium Dome and the extension of London Underground's Jubilee Line were all built by workers who had been checked against the list.

It filtered a multi-billion-pound industry, but it was run by a husband-and-wife team from a tiny office in the Midlands. Ian Kerr was in charge, helped by his wife Mary. Mr Kerr died last year, and now she says she is "the only person alive who knows the truth" about the blacklist.

'Weed out troublemakers'

She says it was designed to protect the industry from the labour problems that dogged it through the 1970s and 80s.

"The construction industry was caught out badly in the 1970s and as a result of that they were determined to weed out any troublemakers," she said.

Blacklist Britain will be broadcast on Monday 10 June at 20:30 BST on BBC One BBC One - Panorama: Blacklist Britain

The office was raided in 2009, and only then was the scale of the monitoring revealed. The files are not just employment records and National Insurance numbers; they are highly personal and go back decades, containing details of relationships, even personal comments such as a worker being described as incompetent and "a bit of a sheep".

Mrs Kerr defends the list, saying: "Unfortunately there are people in this life who do cause trouble. I can't say whether people on that list caused genuine trouble but certainly I know some of them would have."

But she now says she is sorry if anyone was kept out of work as a result of the list.

The list also contained mistakes. Mr Nolan finally got to see the file that was denying him work. It said he had worked on the Jubilee Line extension, a project notorious for disputes. He never did.

"Just that one page basically: my date of birth, National Insurance and that line off the Jubilee Line and that stopped me working for the past 15 years," he said.

Things have changed since 2009. New laws have been introduced and companies say procedures have been changed.

'Devastating'

But some workers say the problem has not gone away.

"I couldn't get a job cleaning the toilets, I couldn't get a job anywhere in the construction industry,' says Frank Morris, who thinks he's been blacklisted.

In 2012 Frank Morris was working as an electrician for a subcontractor on the £15bn London Crossrail link, Europe's largest construction project.

Mr Morris says that within weeks of starting work he was identified as a union man and the company he was working for had its contract withdrawn.

Panorama has tracked down a man who worked alongside Frank on the site. He was afraid to give an interview for fear of losing work, but he told me he firmly believed that Frank was singled out because he was on a blacklist and that the contract was withdrawn to get rid of Frank.

Crossrail denial

Crossrail told Panorama it vigorously denied what it said were unsubstantiated allegations made by Frank Morris, and told us it had seen no evidence of blacklisting of any kind by contractors involved with the Crossrail project. And because Frank Morris is now pursuing a claim for unfair dismissal, the companies involved said they cannot comment further.

Gail Cartmail, of Unite, says the union has seen evidence that suggests blacklisting continues in the construction industry.

I know I'm going to have another 26 years of being blacklisted… it's going to carry on Howard Nolan

"There's evidence that blacklisting is a contemporary problem and while I think it's unlikely that the industry would set up an organisation like the consulting association again there is evidence that people are active and busy vetting and comparing names to lists they hold," she said.

The Information Commissioner's Office, whose job it is to protect data privacy, says it has seen no evidence of a new blacklist in the construction industry.

Frank Morris continues to campaign to get his job back. He says life is hard for his family.

"We had no money to pick the kids up from school. And [my wife] she's just screaming at me, 'What have you done? What have you done?' It'll break a family."

Howard Nolan, the electrician who lost years of work on the basis of incorrect information on a secret blacklist, says he'll never escape.

"It's never going to go away. I've got another 26 years if I retire at 65, but I know I'm going to have another 26 years of being blacklisted … it's gonna carry on."

You can watch Panorama: Blacklist Britain, on 10 June at 20:30 BST on BBC One. Or catch up later on the BBC iPlayer.