Sorry, Tony. The ID cards vote was the easy part

MPs voted to approve the Government's controversial national identity card scheme last week, to the relief of Tony Blair, if not of civil liberty campaigners and rebel backbenchers. But now comes the hard bit. How will the scheme work? Or more to the point, can it work?

Officials have been carrying out a "market sounding exercise" in recent weeks, to gain feedback from the software companies that will implement the scheme. The response has been mixed. ID cards cannot be introduced by 2008, all say. The scheme is too complex, most say. More worrying, some of the brightest minds in the software industry still have no real sense of what the Government actually wants to achieve from a policy in development since 2002.

The Government has justified the scheme by claiming the biometric cards will tackle identity fraud, illegal immigration and terrorism. But Robin Wilton, corporate architect for "federated identity" at Sun Microsystems, says this is the wrong approach: "This will not make people trust the scheme or want to enrol. The Government should look for positive uses that will directly benefit users."

For example, ID cards could be used to provide online electronic signatures for official documents, such as employment contracts or conveyancing forms.

So far, we can fit what we know about the scheme on the back of one of the cards (assuming they are small, of course - no one knows what size they will be). The card will carry biometric information about its owner, probably including all 10 fingerprints, both iris scans and a facial scan. Most companies think this is too complex. Ian Williamson, vice-president of Computer Sciences Corporation in Europe, says it may be simpler - and safer - to scan and store records of the skin pores on fingers instead of fingerprints, which are not always a reliable means of identification.

Manual workers' fingerprints may get worn down, for example, while arthritis sufferers may have difficulty rolling their fingers on to pads to have their prints checked. Mr Wilton at Sun Microsystems points out that facial characteristics, too, can change in the course of a lifetime.

The more complex ID cards are, the less likely that they will be delivered on time and on budget. Mr Williamson adds: "The Government needs to ask if it is making life too complicated by requiring all 13 biometrics and storing a large amount of data about each citizen. The system has to be robust and fast."

One supposed advantage of a biometric card is that only its holder can use it. But the Home Office has not said how, and how often, the biometrics of the card carrier will be scanned to check they match those featured on the card. Will police carry portable scanners for stop-and-search checks? And how will the cards work at airports - particularly overseas? Again, no one knows, mainly because the Government does not yet know for what, and where, they will be used.

Mr Wilton at Sun Microsystems says that the Government has got to decide what it wants before it asks companies detailed technical questions. But so many competing departments and organisations are trying to get in on the act that this will not be easy. With the immigration service, social security offices and police forces - among others - all wanting to store and access information on the cards, the requirements for their implementation are far from straightforward.

One final question is cost. By default, this could prove to be the determining factor. The Home Office claims a new passport and identity card will cost the user £93, or £5.5bn in total over 10 years. This will probably force the Government to streamline the scheme radically.

But however much is spent, ID cards can never be 100 per cent certain to work. As John Newton, government consultant for the electronics giant Fujitsu, warns: "It's like saying it's impossible for planes to crash."