The personal details of every prisoner in England and Wales have been lost by a government contractor in Britain's latest data security breach.

Police were called in after a consultancy firm working for the government lost a computer memory stick containing the names and date of birth of 33,000 prison inmates with six or more convictions and people on drug rehabilitation programmes.

This follows the loss of secret intelligence files, information about millions of child benefit claimants and details about learner drivers.

Last year, Prime Minister Gordon Brown ordered an urgent review after the tax authority HM Revenue and Customs said it had lost data on 25 million people, exposing them to the risk of identity theft and fraud.

The Home Office (Interior Ministry) said it had encrypted the prisoner data before passing it to PA Consulting Group, a London-based management consultancy firm. No one at the company was available to comment.

The Home Office said it had ordered an immediate investigation into the loss, which Conservative Shadow Home Secretary Dominic Grieve described as a "massive failure of duty".

"A full investigation is being conducted," a Home Office spokesman said. "Police and the Information Commissioner (Richard Thomas) have been informed."