The success of the government's national ID card plan is threatened by its reliance on untried technology and costs spiralling beyond the current £5.5bn estimates, warn experts.

The scheme has faced an outbreak of criticism coinciding with the second reading of the proposed legislation in the House of Lords this week.

A report from the London School of Economics concludes that while there are potential benefits from a national ID scheme, the current proposals are 'neither safe nor appropriate'.

'The proposals are too complex, technically unsafe, overly prescriptive and lack a foundation of public trust and confidence,' says the report.

'The concept of a national identity system is supportable, but the current proposals are not feasible.

'No scheme on this scale has been undertaken anywhere in the world ? smaller and less ambitious systems have encountered substantial technological and operational problems that are likely to be amplified in a large-scale, national system.'

The government has also underestimated the cost of the necessary security and of the technology itself, says the report.

'Registration alone (could) cost more than the projected overall cost of the system,' it says.

The Association for Payment Clearing Services (Apacs), which is responsible for the rollout of the £1.1bn chip-and-PIN bankcard scheme, is also warning that the budget could be tight.

'£5.5bn is a lot of money, but it could well be tight because of what the Home Office is doing with biometrics ? it's using a brand-new technology, rather than using something already out there,' Apacs chief executive Paul Smee told Computing.

The Lords Constitution Committee report on the bill, published last week, also emphasised the uncertainties around the cost and technical side of the scheme.

But politics is now likely to scupper the progress of the bill's passage into law. If the general election goes ahead on 5 May, as is widely predicted, the ID cards bill will be held over until the new Parliament.

One of the roles former Home Secretary David Blunkett is to undertake as part of his return to frontline politics is to publicise the ID card plan, despite the likelihood the bill will not get passed before the election.