The Home Office memory stick lost by a PA Consulting contractor a year ago contained 250,000 more names than originally disclosed.
The Home Office resource accounts state that the memory stick contained the personal details of 377,000 individuals from the Police National Computer (PNC) and prison records. The Home Office earlier said the number was 127,000.
The data on the extra 250,000 records comes from the Drug Interventions Programme and is an estimate of the number of times the programme was accessed by individuals, according to a Kable report.
The actual number of people whose data was lost will not be as high as the number of records, and only their initials were recorded, limiting their risk of exposure.
The incident was investigated and reported to the Information Commissioner's Office.
PA was fired over the loss of the memory stick, which has not yet been found. The company was still the top earner among Home Office consultants. It took home £24.5m, a quarter of what the Home Office spent last year in total on advisors.