The Home Office has had to dramatically revise its estimates of the amount of data contained on a memory stick lost by third-party contractor PA Consulting last year.

The department's newly released Resource Accounts for 2008-09 (PDF) say that the USB device containing Police National Computer and prisoner data actually held 377,000 records, 250,000 more than originally reported.

The revelation will raise further question marks about the ability of government to safeguard the data of its citizens, especially when that data is being handled by third-party consultancies.

New information released yesterday showed that the Home Office paid PA Consulting a whopping £24.5m last year, up from just £8.4m the previous year, owing to its work on the National Identity Scheme and the Interception Modernisation Programme.

After the data breach last year, however, the Home Office terminated its contract with PA Consulting, and carried out "a full review of the system and procedures" that led to the breach.

"The department will continue to monitor and assess its information risk in the light of these events, in order to identify and address any weaknesses and ensure continuous improvement of its systems," said the Home Office report.

A Home Office spokesperson said that the extra lost records came from users of the Drugs Interventions Programme, according to government news site Kable.