By Nick Assinder
Political correspondent, BBC News website
Cards are to be compulsory for passport applicants from 2010
The creation of a giant register of every card-carrying member of the British public was always one of the more controversial elements of the ID cards proposal.
The missing data crisis could not have provided a more spectacular example of what might happen if such databases are not secure.
It has sparked widespread fears over the security of personal information and raised the inevitable demands for the entire ID card scheme to be abandoned - with signs the government may now be having second thoughts.
The legislation has already been passed by Parliament, despite some severe cross-party reservations.
But the campaign against it, backed by the opposition parties and civil liberties groups, has been given fresh impetus by the data crisis.
Now might just be the last chance the prime minister gets to put this whole thing onto the back burner, or trim it in an attempt to answer some of the biggest criticisms.
A tactical retreat at this point, after reviews of the system and the new inquiries already launched by Mr Brown into what went wrong with the child benefit information, might cause far less damage than seeing a top-level and possibly growing revolt against the proposal - specifically the pledge to eventually make the cards compulsory - up to the next general election.
That election, even delayed until the last moment, is still far too close for ministers to feel at all confident the data crisis will not still be fresh in voters' minds.
Indeed it is likely that any Labour manifesto commitment to making the scheme compulsory would see the Tories turning it into a key election platform around the bigger issue of competence.
For the moment, ministers insist ID cards would be essential in stopping just the sort of identity theft and fraud which might be carried out by anyone using the child benefit information illegally.
But Tory leader David Cameron has said voters will think it is plain "bizarre and weird" if Mr Brown does not at least have another look at the proposals.
Liberal Democrat president has said: "We need to assess the stupidity of that proposal early so we don't waste any more public money going down that completely unhelpful road."
They have been joined by some senior Labour MPs, including Karen Buck, a member of the Commons home affairs committee, and Andy Love, a member of the Treasury committee.
Both have suggested it is time to stand back and have a period of reflection over the proposals.
Perhaps crucially, the information commissioner, Richard Thomas, has urged ministers to review the amount of data they intend to amass on the national identity register.
And some in Westminster were pointing to Gordon Brown's words during question time in which he told David Cameron: "What we must ensure is that identity fraud is avoided, and the way to avoid identity fraud is to say that for passport information we will have the biometric support that is necessary, so that people can feel confident that their identity is protected."
Some have read that as a sign Mr Brown might be ready to abandon any plans to make ID cards compulsory, widely seen as the only way to ensure they are effective.
It is even being speculated he is ready to make do with biometric passports which are gradually being rolled out, with no immediate move to go further down the road to ID cards.
Under the current legislation, everyone over the age of 16 applying for a passport will have their "biometric" details - including fingerprints, eye or facial scans - added to a national identity register from 2008.
The first identity cards will be issued in 2009 to those wanting one, but from 2010 anyone renewing or getting a passport will have to get one.
It would be possible for the prime minister to go no further than the first - passports - phase of the scheme and delay moving to the further steps indefinitely if necessary.