Paul Pindar, chief executive of Capita, said the group that administers London's congestion charging scheme was "cautious" about running such a system. "There are a number of issues around identity cards which we would need to consider very carefully in terms of what Capita's stance would be on the project."
These are understood to relate to security, civil liberties and reputational risk.
Serco, which runs the UK's ballistic missile tracking and warning system, and also bid to run the London congestion charging scheme, said that while it already offered biometrics and had the "technology to rise to the challenge of delivering a national identity card scheme", it would view a contract as "an opportunity that probably carries more risk than some of our more conventional contracts".
Serco said it would have to evaluate any contract very carefully, considering not just the technical and commercial issues but those around security, civil liberties and reputation, although it stressed that some of these issues "will not be ours to address".
The caution raises doubts about the viability of involving the private sector in delivering a national identity card scheme. The government intends 80 per cent of the economically active population to have voluntarily signed up for such a card by 2013 by applying for one of the new biometric passports or driving licences.
The Home Office plans this month to choose a "development partner" which will design the project and support Home Office tests. A contract to construct the database that will hold personal information will be advertised later.
Information technology services groups such as Atos Origin, Cap Gemini and Electronic Data Systems have been talking to the Home Office about how to build the database. Neither Capita nor Serco are believed to be involved. Atos, which is running a trial for the Passport Service, would be interested in running a national scheme.
The development partner will not necessarily run the scheme although it could be in a strong position. The Home Office said work was not yet at the stage of determining how the system would be run.