Experts have warned that the ID-card scheme risks being derailed by mistakes in fingerprint matches.
The £4.4bn National Identity Scheme's (NIS's) reliance on fingerprint and facial-recognition biometrics exposes the system to error, according to the independent Biometrics Assurance Group (BAG).
BAG urged the Identity and Passport Service (IPS) to adopt iris scans as a 'fallback', for when there are problems taking or matching a fingerprint.
BAG claims that 'exception handling' — dealing with mismatched or unclear fingerprints — would occupy a large amount of NIS's resources, putting the technology, delivery and costs under strain.
The IPS is putting an enlarged fingerprint bureau in place to ensure that exceptions can be handled but said iris scans are unlikely to be part of the scheme for the near future.
The BAG annual report stated: "BAG was particularly concerned with the plans for exception handling. Exception handling has a large impact not only on the technical elements of the scheme but on business processes."
BAG claimed there are four million people aged 75 or over in the UK and warned it is hard to take clear fingerprints from this group.
But the IPS said that price was likely to rule out iris biometrics.
An IPS spokesman said: "It is unlikely that iris scans will be used in the scheme. Suppliers can use whichever biometric they choose in their solution but they will have to show it meets minimum standards and provides cost benefits."
BAG also called for more research into exception handling; guarantees on compliance with the Data Protection Act and rules on data sharing; robust controls on access; and interoperability of subsystems.
The ID-cards scheme will be rolled out over the next four years, starting with about 10 million 'critical' workers in 2009, young people in 2010 and the rest of the UK public in 2011/12, when people will have a choice of a passport or ID card.