"Crossrail Limited is not aware of, and has seen no evidence of, blacklisting of any kind in connection with the Crossrail project," Wolstenholme said. "If Unite has any evidence then we wish to see it; we have made this point a number of times and yet none has been forthcoming. Crossrail has written to the trades unions on several occasions setting out our commitment to taking firm, decisive and immediate action if any substantive evidence can be presented."

Wolstenholme added: "All contractors working on the Crossrail project must comply with the Employment Relations Act 1999 (Blacklists) Regulations 2010 which explicitly outlaws the blacklisting of construction workers. All our contractors are fully aware that blacklisting is unlawful as well as being a breach of contract which would result in immediate action by Crossrail."

Crossrail stated that the Consulting Association was closed down in 2009 following enforcement action by the Information Commissioner, well before the award of the first tunnelling and station contracts in December 2010.

In December 2012, Vince Passfield, Unite’s deputy regional secretary for the London and eastern region, said: "Imagine Unite’s horror in hearing that Crossrail contractors met with the Consulting Association, the organisation that compiled a blacklist of mainly construction operatives. The Consulting Association was raided in 2009 by the Information Commissioner’s Office."

Unite stated that it is in the public interest that this matter is properly investigated by Transport for London and that the Crossrail board is held to account for the implementation of good workplace practices. Unite has campaigned strongly against what it considers to be the anti-union bias that exists across the whole project, which is expected to see the first trains running in 2018.