Tony Blair relaunched the government's controversial identity card bill in May, claiming biometric cards are needed to tackle the growing problem of identity fraud.

The prime minister said the ID cards would be phased in from 2008 before being made compulsory. But experts again raised doubts about the effectiveness of a scheme expected to cost £585m a year to run.

Peter Dorrington, fraud expert at SAS Institute, said biometric technology on this scale is untested. "If you include any manual element you create potential for error, corruption and coercion," he said.

The Tories said the technology's robustness had to be proven before they would support the bill.

A new survey of over 1,000 UK consumers by voice verification specialist Intervoice found that only 10 percent of the public are willing to pay for identity cards. "People do want to be protected, but not inconvenienced," a spokesman said.