Around 100,000 construction workers are to be vetted using biometric face and palm recognition screening during the building of the London 2012 site.

The two-tier biometric access system, which includes palm print reading and face recognition as each worker enters the site, is part of a £354m security strategy for the 500-acre Olympic park during its construction, which starts in June.

But it has raised concerns about data protection among unions and civil liberty groups.

Alan Ritchie, general secretary of Ucatt, the main construction union, said he wanted assurances from the Olympic Delivery Authority that the data would not be shared and would be wiped once the project is complete.