The premier challenged Michael Howard to back the plans, reminding him he had supported ID cards in the past.

The Conservatives have said they will join the Lib Dems and some Labour MPs in opposing the cards unless ministers "conclusively prove" they are needed.

Critics say ID cards are expensive, ineffective and curb civil liberties.

The Home Office has estimated that ID theft costs £1.3bn a year in the UK.

New protections?

Home Secretary Charles Clarke unveiled the latest Identity Cards Bill on Wednesday.

He says he accepts genuine worries were raised about the previous bill, which was dropped ahead of the election.

Home Office Minister Tony McNulty said: "A secure compulsory national identity cards scheme will help tackle illegal immigration, organised crime, ID fraud, terrorism and will benefit all UK citizens."

Earlier this week, Mr Clarke urged Labour MPs opposed to the scheme to examine proposed "safeguards" in the bill.

He also offered to meet critics to discuss their concerns, which are centred on civil liberty issues.

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Changes to the bill include giving more powers to the watchdog charged with overseeing the scheme, as well as new limits on government agencies' access to the National Identity Register.

Inconvenience

It is now estimated that the cost of buying a new national ID card will be £93 per person - the previous figure was £88 but had not included VAT and other extras.

Earlier the prime minister's spokesman said the longer the debate had run, the more people had seen the benefits of ID cards in tackling illegal immigration, organised crime and abuse of public services.

"People are recognising that identity is just as valuable as possessions," he said, suggesting it could take 60 hours to restore a stolen identity.

The spokesman said the biometric data on the cards, such as iris and face scans or fingerprints, will be needed for future passports in any case.

The Conservatives initially voted for the ID card legislation in the last Parliament but abstained in the key Commons vote, saying the plans had to pass five tests.

The tests included issues connected to the technology and a call for the bill to "clearly define" the purpose of the cards.

'Extreme doubts'

The government says the new legislation answers concerns raised by Conservative shadow home secretary David Davis.

On Monday Mr Davis stood by his party's stance and said he could not currently recommend his party supported the bill.

"On an issue of this importance, one that represents such a fundamental change in the relationship between the citizen and the state, the government must make the case and conclusively prove the need for such a change," he told MPs.

Liberal Democrat spokesman Mark Oaten said if the Tories joined the Liberal Democrats and some Labour MPs in opposition to the measures, "we could defeat the ID card scheme".

Senior backbencher Gwyneth Dunwoody said some Labour MPs were uneasy about the scheme as government had sometimes used information about people's lives "for the worst possible reasons".

A spokesman for the T&G union said ID cards were an "enormous, costly and unnecessary diversion".

Liberty's Shami Chakrabarti urged MPs to reject what she said was a "rehashed bill that is more about political machismo than rational policy".