Mr Thomas also expressed concern over the Office of National Statistics' forthcoming Citizen Information Project, which will create a database to act as a UK population register, and plans under the Children's Bill to create a database that is intended to identify, and hold information on, every child in the UK.
The Government's proposals for the UK identity card, published in April, include draft legislation that would allow for a database to be kept containing detailed personal information on cardholders - such as name, gender, address, all previous addresses, photograph, fingerprint, and NI number - and also extensive records tracking an individual's use of his card.
In particular these records would, according to the draft Bill, include "particulars of every occasion on which a person has accessed an individual's entry and of the person who accessed it".
Thus, for instance, if an individual cardholder uses a service during which the service provider checks identity or entitlement, then there would be a record that links the service provider with the cardholder.
If the Government is successful in bringing the draft Bill into law, and establishing the ID Card system, the provisions will create an electronic fingerprint of everyone who uses a service that requires an ID Card check. It will in turn create pointers to sources of detailed information, held by the service provider, about the services used by each UK citizen.
Law enforcement agencies and security services would be given wide access to these records.
Thomas stressed that his concern relates not to the ID cards themselves, but to the information that will be gathered and stored as a result of it. Speaking about the proposed national register, he explained:
"Some of my counterparts in Eastern Europe, in Spain, have experienced in the last century what can happen when government gets too powerful and has too much information on citizens."
The problem here, explained Thomas, is that the Government has not properly explained what the card is supposed to do. He told The Times:
"The Government has changed its line over the last two or three years as to what the card is intended for. You have to have clarity. Is it for the fight against terrorism? Is it to promote immigration control? Is it to provide access to public benefit and services? Various other reasons have been put forward . . . I don't think that is acceptable."
His comments come in the wake of a recent report into the ID scheme by the Home Affairs Select Committee. This, published at the end of July, approved the plans in principle, but warned of serious shortcomings in the detail of the proposals, and found some elements of the Government's draft legislation "unacceptable".
The Committee's main concern was similar to that of Richard Thomas – not the ID cards themselves, but the fact that the draft Bill goes much further than necessary to introduce a simple system to establish and demonstrate identity.
Responding to the criticisms, a Home Office spokesman told the BBC, "There will be no question of a card scheme being an infringement of human rights - protection of privacy, strict limits on the information held, its use and disclosure, and ensuring independent oversight will be built into the legislation."
At a press briefing, the Prime Minister's Spokesman said that Mr Thomas had made an important contribution to the debate on ID cards.
"There would be guarantees against any 'function creep' regarding the transfer of information about people to different parts of Government," said the spokesman, adding, "There would be proper oversight of such a scheme, as you would expect."
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