Tony Blair has promised he will listen to concerns about plans for identity cards after seeing his Commons majority slashed from 67 to 31 on the issue.
The vote was the first proper test of Labour's reduced majority
Twenty Labour MPs rebelled against the plans on Tuesday night and senior MPs say changes will be needed to get the plans through Parliament.
At prime minister's questions, Mr Blair said: "We will have to listen to those concerns and respond to them."
But he urged critics to recognise the case for secure ID cards in the UK.
As well as helping to tackle organised crime, terrorism and illegal immigration, they could bring benefits to citizens, argued Mr Blair.
Much of the work towards the ID card system would be needed in any case for biometric passports being taken up by other countries.
Liberal Democrat leader Charles Kennedy said there was disquiet over many parts of the plans.
His party says the scheme could be Mr Blair's "poll tax".
The ID cards vote was the first proper test of a key policy area in the Commons since Labour was returned on a reduced majority.
Those who voted against the scheme included: ex-International Development Secretary Clare Short and former ministers Glenda Jackson, Kate Hoey and Mark Fisher, plus two new MPs Linda Riordan and Katy Clark.
The bill, which now faces a tough time in its committee stage, secured a second reading by 314 votes to 283.
John Denham, who was chairman of the Commons home affairs select committee in the last Parliament, warned further opposition lay ahead.
He told BBC News: "I think the government is going to have to make a number of changes to its approach to the bill to be sure of getting it through."
Greater controls needed
Mr Denham continued: "I think the scale of unhappiness is wider than the number of people who rebelled last night."
He backed the bill, but said ministers had not properly explained to the public how the scheme would work.
He said the aims of the measures needed to be more clearly defined. There needed to be greater controls over access to the information by police and other authorities.
He also thought the commissioner overseeing the scheme needed more powers.
One of the 20 rebels, Labour's Bob Marshall Andrews, predicted that ministers would eventually drop their ID proposals.
In the debate, Home Secretary Charles Clarke said ID cards would help counter, not create, a "big brother society".
He tried to address fears that the cost of ID cards would prove prohibitive for citizens by offering a cap on the price - although he has not given the figure.
He said there would be no compulsion on anybody to show their ID card in the street and stressed that people would have the right to check data held on them.
New passports including biometric data, such as iris scans, fingerprints and face scans, would cost £60-65 to produce, with the ID cards costing only about £30 extra, he said.
Mr Clarke branded a London School of Economics report which estimates a card would cost up to £300, "technically incompetent".
Conservative shadow home secretary David Davis said people were more likely to trust independent cost estimates than a government which had let previous computer projects overrun their budgets.
He said a future Tory government would scrap identity cards, adding that Labour's legacy would be "surveillance from cradle to grave".