Plans for introducing ID cards in the UK are poorly thought out and vital details are still unclear, say MPs.
ID cards remain a controversial issue
The Commons home affairs committee says ID cards should go ahead and can help fight organised crime and terrorism.
But it criticises a "lack of clarity" over how the scheme will work in practice, with too much information kept secret by ministers.
Shadow home secretary David Davis said the plans were "incoherent, ill thought through" and 10 years from realisation.
The first ID cards carrying biometric data, such as fingerprints and iris scans, will appear in 2007 and the Home Office wants them made compulsory by 2013.
The official committee report says ID cards can make a significant contribution to fighting crime and coordinating access to public services.
The scheme will change the relationship between citizens and the state, but potential benefits outweigh such concerns, it says.
"However, the introduction of identity cards carries clear risks, both for individuals and for the successful implementation of the scheme," it continues.
On several counts, the MPs say the proposals of the "unprecedented" scheme are unclear.
More details are needed, for example, on how many card readers and biometric readers will be needed to check ID cards or how much they will cost, they argue.
The committee also complains the draft legislation "goes far wider than is necessary to introduce a simple system to establish and demonstrate identity".
They back civil liberties campaigners' fears about how many people will be able to access personal details on the ID register without the person concerned knowing.
Two MPs on the committee, Labour's David Winnick and Liberal Democrat Bob Russell, voted to reject ID cards on principle.
Facial scanning: A camera with appropriate software records face contours and converts them into code. A computer processes the data and checks against stored record.
Iris imaging: Software scans a digital image of the iris to compare its unique pattern with all those stored.
Fingerprinting: A scanner reads the ridge patterns and compares the converted code with those on a database.
Mr Russell said the unknown cost of the scheme, which could be "several billions", would be better spent on police recruitment and surveillance.
Information Commissioner Richard Thomas told BBC Radio 4's Today programme his main concern was with the national register behind the cards, and the personal information on it.
Too many bodies, such as Inland Revenue, had access to this information, but the draft bill took away the individual's right to see it, he said.
He said: "We want to see very precisely on the face of the bill what these cards are going to be used for and we're pleased the committee has asked for the same approach."
Committee chairman John Denham said the ID scheme should go ahead but ministers had to take serious note of the MPs' criticisms.
He told Today the main worry was that key decisions about the scheme's design may be taken by the private companies working with the government, rather than in a transparent way.
"With an open procurement process, with proper public and technical scrutiny, we can make sure this project goes right and we need it to work," he said.
But Home Secretary David Blunkett said the desire for more information had to be balanced against getting best value by keeping market-sensitive details of contracts confidential.
Mr Blunkett said the government was at the early stages of an ambitious project and welcomed constructive discussion of the plans.
"ID cards will bring enormous benefits to us as individuals and as a society," said Mr Blunkett, who was pleased the MPs believed it was possible to deliver the scheme on time and to cost.
For the Tories Mr Davis said the plans could end up being "fatally flawed".
The government had never said whether the cards were for fighting terrorism, illegal immigration or benefit fraud, he told Today.
"There may be an argument for an ID Card but it has to be done very carefully to deliver the outcome we want in a cost-effective manner," Mr Davis said.
An idea with such a potential impact on civil liberties should not be left to a Home Office civil servant to decide, it must be subjected to parliamentary scrutiny, he added.
Owen Blacker, from internet privacy group Stand, warned the cards threatened personal privacy and could be a "technological disaster".