Blacklisting campaigners celebrated yesterday after a former construction boss was told his evidence "defied belief" at a parliamentary committee hearing.

Pat Swift, who was head of HR at construction giant BAM from 2004 to August 2013, appeared in front of the Scottish affairs committee over his role in the use of blacklists run by The Consulting Association (TCA).

During the hearing Ian Davidson MP had to remind Mr Swift he was speaking under oath, while Jim McGovern MP labelled him "one of the most evasive witnesses ever."

Other MPs on the cross-bench committee expressed shock at attitudes expressed by Mr Swift, who was leading the BAM-Ferrovial-Kier Crossrail consortium when it dismissed Unite shop steward Frank Morris in September 2012, allegedly because of his union activities.

In an evidence session lasting nearly two-and-a-half hours Swift admitted being the "main contact" with TCA between 2004-2009, saying that his staff were in "constant communication" with the organisation.

However Mr Swift claimed he was unaware TCA provided a blacklist service and never used it to red-flag "problem" employees, maintaining that he thought the TCA was a "general referencing service."

Lyndsay Roy MP asked Mr Swift about his involvement in the sacking of Mr Morris.

Mr Swift initially claimed he couldn't remember but later admitted he ordered Mr Morris's dismissal because "this guy had been on a demonstration."

Graeme Morrice MP was incredulous, asking: "A perfectly legal demonstration against an illegal blacklist?"

MPs also raised the example of Mickey Guyll, a crane driver for BAM-Nuttall during the construction of London's Docklands Light Railway.

Mr Guyll was added to the blacklist after he became a safety rep following the death of a co-worker on site. Mr Swift's attempts to play down his involvement in the matter were met with scepticism by MPs.

In a statement after the hearing, a Blacklist Support Group spokesperson said: "We have been campaigning against the blacklisting of trade union members on the Olympics and Crossrail for over four years.

"The Scottish affairs select committee has vindicated everything we have said. We salute all the MPs on the committee for exposing the truth."