Justice minister Jack Straw has ordered an inquiry into the loss of a portable hard drive containing the details of 5,000 prison staff.

The disc was lost by IT supplier EDS, which has successfully bid to be part of the National Identity Card Programme.

"I am extremely concerned about this missing data," said Straw.

"I was informed of its loss by the News of the World and have ordered an urgent inquiry into the circumstances and the implications of the data loss and the level of risk involved.

"I have also asked for a report as to why I was not informed as soon as my department became aware of this issue."

The loss raised fears that, should the information fall into the wrong hands, ex-prisoners could be able to track down prison staff. The drive was last seen in July 2007 by EDS staff.

"EDS can confirm that a hard drive containing data relating to the Ministry of Justice (MoJ) has been lost," said a spokesman for the company. "We take this matter very seriously and we are working with the MoJ to confirm the level of risk and provide a detailed analysis of the situation and remedies that should be undertaken."

The Data Handling Review, commissioned in the wake of the loss of discs containing 25 million child benefit records to improve government information security, specified that all standards should apply to third-party contractors as well as government departments.

The Information Commissioner's Office said it was aware of the loss and had been in touch with the Ministry of Justice, though it will not have any specific role in the inquiry.