Shadow home secretary Chris Grayling said the project would be "scrapped immediately" by an incoming Conservative government.

He said: "I am increasingly concerned that the government is putting in place contractual arrangements that are designed to tie the hands of a future government and I want to make the contractors absolutely aware that we do not intend to complete this work."

Bidding for the contracts is surrounded by secrecy, but it is thought that Manchester-based 3M SPSL and De La Rue are among those trying to win the lucrative contract.

The £6bn project, which if rolled out across the country will be the biggest security printing job in history, has been surrounded by controversy with unions and civil liberties groups united in their opposition.

It is due to be trialled in Manchester as a voluntary scheme in the autumn, with a nationwide roll out scheduled for 2012.

It was reported at the weekend that new home secretary Alan Johnson has ordered an urgent review of the scheme.