The prime minister faced questions in the House of Commons last week on two of the government's major IT-related programmes.
Menzies Campbell, acting leader of the Liberal Democrats, asked Tony Blair about a reported three-year delay on the Impact (Intelligence Management, Prioritisation, Analysis, Co-ordination and Tasking) programme to help police forces across the UK share intelligence information.
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The Home Office's Police IT Organisation was involved in setting up the Impact programme after the Bichard Inquiry into the murder of schoolgirls Holly Wells and Jessica Chapman in 2003.
Officials have found that Impact is proving more complex to deliver than first thought. And IT suppliers' trade association Intellect last week expressed concerns about delays.
In the Commons, Campbell asked Blair when he expected Impact to be fully functional. Blair said he was unable to answer the question "off the cuff", but undertook to write to Campbell.
This answer prompted Richard Bacon, a member of the Public Accounts Committee, to question whether the technology supporting ID cards would work.
Bacon said, "The prime minister could not explain the reasons for the police computer delay in answer to an earlier question. Why, then, should we believe what he says about identity cards, given that they are above all else a government computer project?"
When Blair did not answer the question directly and instead gave a justification of ID cards, Bacon interrupted. "What about the computer project?" A chorus of MPs called on Blair to answer Bacon's question.
Blair replied, "On the subject of computer technology, let me say that it is not as if, in respect of either passports or identity throughout the Western world, there are not well-tried systems for identity cards."
He accused the Conservatives of "raising issues related to computer technology as a smokescreen for their true opposition" to ID cards.
Afterwards, Bacon said that Blair's response raised questions about why the UK was not seeking to buy systems used in other countries.