James Hall, chief executive of the Identity and Passport Service, said the system would be voluntary at first, to allow groups to speed up background checks. “Whether every group would think that was a cost- justifiable expenditure I don't know,” Hall said. “No doubt as demand grows prices will fall. Maybe in 10 years time people will think that's a justifiable expense and entirely appropriate.''

Hall was speaking after the government invited bids for two billion pounds ($4 billion) of work on the project, which ministers say will cost 5.7 billion pounds over the next decade. Civil liberties groups say the IDs will invade privacy.

“The government hasn't really explained to anyone how ID cards will work,” said Gareth Crossman, director of policy at human rights group Liberty. “They always avoid giving the detail about what will be necessary to check someone's identity. When you look at the benefits, they're very small compared with the financial and social costs.''

The checks are designed to prevent repeats of incidents like the one in 2002 when Ian Huntley killed two 10- year-old girls attending the primary school where he worked.

The Home Office minister Liam Byrne, said in June, that using ID cards to verify the identity of applicants may cut the time it takes to conduct a criminal record check to four days from the current four weeks.