Tony Blair will miss today's crucial Commons vote on ID cards after being held up in South Africa, Downing Street announced today.
The Prime Minister was due to return from a summit in Pretoria this morning, but a problem with his plane means he will not now be back until tomorrow morning.
A Downing Street spokeswoman said: "The Prime Minister won't be back until tomorrow morning. He was due back this morning, but one of the engines in the plane malfunctioned last night before take-off."
Chancellor Gordon Brown said he expected the Government to win tonight's vote on ID cards, even in the absence of Mr Blair.
Mr Brown told the BBC Radio 4 Today programme: "I think we are starting to convince people. I think the public are more convinced than some of the politicians in the House of Commons.
"The central issue here is the right to your own identity, that your identity should be secure and it shouldn't be stolen and it should be protected."
Biometric systems were increasingly being used by private sector companies such as banks and credit card issuers to ensure security, said Mr Brown.
"I think people generally accept that for entry to the country with passports, it is right to use the most modern and sophisticated and secure means of identity," he said.
"The question then is if we are to protect your and my identity, are we not right to use the best and most modern secure means of identification?
"The issue for me is can there be individual safeguards for individual citizens and can there be proper accountability to Parliament."
Mr Brown said that one of the September 11 terrorists had been shown to have used 20 separate identities.
"It's absolutely crucial to the disruption of terrorism that we can spot quickly where multiple identities have been used," he said.
He denied that the current legislation would make the cards compulsory, saying that this would require a separate Bill being taken through Parliament at a later date.
The Prime Minister had cut short his trip to South Africa in order to return for today's vote.
Ministers hope a series of concessions on ID cards will be enough to minimise a Labour rebellion and avert a Commons defeat that could be devastating to Mr Blair's authority.
The Prime Minister missed a crucial vote on religious hatred laws last month, which saw the Government slump to only its third Commons defeat - by just one vote.
Downing Street dismissed that embarrassing lapse as a "one-off" and said the Prime Minister would "make sure" he was present for important votes in the future.
Today's vote on ID cards will be followed on consecutive days by further battles over the smoking ban and controversial proposals for an offence of "glorifying" terrorism.
Arguments over the terror laws have descended into a major party political row - with the Tories accused of being soft on terror and the Government of "ineffective authoritarianism".
The Lords altered anti-terrorism legislation in a bid to tighten the offence and prevent it criminalising people not intended to be caught by the law.
But Home Secretary Charles Clarke insists the phrase is one used by the United Nations and should be included.
Between the two conflicts over security measures, MPs will vote on whether to extend a ban on smoking to cover all pubs and clubs.
The Government originally proposed an exemption for pubs serving food and private clubs but came under enormous pressure to impose a universal ban instead.
To avoid almost certain defeat, the vote was made a "free" one for Labour MPs who are expected to extend the no-smoking rule to all pubs and possibly also to private clubs.
The concessions put forward on ID cards would force the Government to introduce a new Bill before it could be made compulsory to be on the national database.
Initially, only people getting a new passport or renewing one would be obliged to have their details recorded.
Ministers will battle to overturn a Lords amendment making the scheme entirely voluntary - removing even the link with passports.
The cards will store fingerprints and other "biometric" data on a microchip which can then be compared with a central database of every adult in the UK.
The Government also gave in to demands for openness over costs, agreeing to an amendment tabled by Labour's Frank Dobson calling for a report to MPs every six months on the price tag.
It will hold back details of the costs until it has agreed deals with private firms for setting up the scheme to avoid prejudicing commercial negotiations.
The London School of Economics has put the total cost of the scheme at £19.2 billion, five times official estimates.
Civil rights group Liberty will be holding a demonstration against ID cards outside Parliament.
Director Shami Chakrabarti, said the Government's "sleight of hand" amendment did nothing to end compulsion.