Privacy advocates have reacted angrily to reports that the government plans to link national identity records to criminal records for background checks on people who work with children and vulnerable people.

Up to 11 million such workers could be affected immediately if the plan goes ahead.

Phil Booth, national co-ordinator of privacy advocates NO2ID, said the move was consistent with the various forms of coercion strategy to create so-called volunteers for national ID cards.

"Biometrics are part of the search for clean, unique identifiers," Phil Booth said. He said the idea was patently ridiculous when the Home Office was planning to allow high street shops and the Post Office to take fingerprints for the ID card.

Following a Freedom of Information Act request to the Criminal Records Bureau, the government admitted to running a feasibility study to link the biometric details to be held in the national identity database to the Criminal Records Bureau (CRB).

The aim was to improve the CRB's accuracy following a recent doubling of errors in fingerprint identification, according to The Register.

NO2ID's general secretary Guy Herbert said ministers had said the ID database would not contain criminal records. "The covert programme unearthed by The Register shows what a fatuous piece of misdirection that is," he said.

"If the CRB gets its way, then for millions of people their ID card would be directly linked to a detailed police record and a scoring system designed to evaluate their suitability for various jobs."

From October, people who work with children and vulnerable people have to register with the Independent Safeguarding Authority (ISA), which uses CRB and other sources to evaluate a person's suitability for the role.

In a written statement a CRB spokesperson said that the CRB committed in its business plan for 2009/10 to research the possibility of introducing biometrics into the disclosure service as a way to improve accuracy.

"This research is still in the early stages of feasibility and several options are being considered as part of this work, including options for the use of ID card data and fingerprints. The CRB is not considering the use of other biometrics at this stage," the spokesman said.

Computer Weekly reported yesterday that the Metropolitan Police is looking for a supplier of portable ID card readers that could work with images of faces, fingerprints and irises.

The ISA's website says it will assess applicants using CRB data, including relevant criminal convictions, cautions, police intelligence and other appropriate sources.

"We will securely store information about people's ISA status for employers and voluntary organisations to use when they are recruiting," it said.