Widespread concern over how effective the £4.7bn National Identity Scheme would be without ID cards being compulsory have been revealed in newly-published project reviews.

The Identity Cards Act passed by the government in 2006 made it clear that ID cards would not be compulsory for British citizens.

But the first Gateway review found that "the police felt that the absence of any obligation to carry or produce identity cards would substantially remove the administrative savings and some of the other advantages that Identity Cards would offer".

The review also noted with some concern, that other users of the scheme in the public sector such as the DVLA, the Passport Agency, the Department of Work and Pensions and the Inland Revenue "were not quite as enthusiastic about the programme as might have been hoped".

The second gateway review, from 2004, shows that the government considered compulsory adoption at an early stage.

"If the conditions are right the first stage of the scheme could then be followed by a move to a compulsory card scheme," says the review. "This step will require full debate and a vote in both Houses of Parliament and will only be taken after a rigorous evaluation of the first stage and when there is high confidence that everything is in place to enable the scheme to work."

In 2006, then Home Secretary Charles Clarke said the cards would become compulsory if Labour won the next election.

But last year, amid widespread opposition to the scheme, the government delayed mass rollout and said cards would not be compulsory, instead targeting foreign national, airside workers and students as the first recipients.

This prompted criticism that the Home Office has lost confidence in the scheme and no longer knew what it intended to achieve.

Home Secretary Jacqui Smith insisted that cards would not be compulsory for other British citizens until public acceptance had been gained.

"While there are big advantages to making ID cards as widespread as possible, we need to be clear there is public acceptance," Smith told the BBC.

A spokesman for the Home Office said the policy on compulsion in the scheme remains the same.

"We believe there will be clear benefits to the scheme becoming compulsory in the future, but we will be in a better position to assess this once it has been running for some time," he said.

"This would take further legislation and would be a matter for Parliament to decide. Any future decision will be informed by evidence of benefits realised from years of the scheme being in operation."

The gateway reviews were published yesterday after four years of legal opposition to the original freedom of information request from government buying agency the OGC at an estimated cost of £120,000.