The Government is under pressure to abandon its ID card plans after one of the main firms involved in the project lost thousands of criminals' personal details.
The names, addresses and expected release dates of all 84,000 prisoners in England and Wales were on a computer memory stick lost by Home Office external contractor PA Consulting.
Home Secretary Jacqui Smith said the loss was "completely unsatisfactory", adding that the information should not have been downloaded on to a memory stick.
The lost computer files also contain the names, addresses and dates of birth of 30,000 people with six or more convictions in the last year, as well as the names and dates of birth of 10,000 offenders regarded as prolific and the initials of people on drug treatment programmes.
"This was data that was being held in a secure form, but was downloaded on to a memory stick by an external contractor," Ms Smith told the BBC.
"It runs against the rules set down both for the holding of government data and set down by the external contractor and certainly set down in the contract that we had with the external contractor."
PA Consulting had the information as part of research it was carrying out for the Home Office on tracking offenders through the criminal justice system.
But the firm is also heavily involved in the ID card project, having been appointed to work on the design, feasibility testing, business case and procurement elements of the programme.
Shadow home secretary Dominic Grieve said: "The public will be alarmed that the Government is happy to entrust their £20 billion ID card project to the firm involved in this fiasco, at a cost of millions of pounds to the UK taxpayer.
Read More
"This will destroy any grain of confidence the public still have in this white elephant and reinforce why it could endanger - rather than strengthen - our security."
