The Ministry of Defence has admitted that more than 11,000 military ID cards have been lost or stolen in the past two years.
Defence minister Bob Ainsworth admitted that 4,433 ID cards disappeared in 2006 and a further 6,812 went missing from July 2006 to December 2007.
Ainsworth revealed the loss in a written answer to Parliament, in response to a question by shadow defence secretary Dr Liam Fox.
The revelation prompted condemnation from opposition parties who said that it made a mockery of security procedures at military facilities and showed a scandalous disregard for the security of British citizens.
In a statement, the Ministry of Defence (MoD) said: "We take the loss of military ID cards very seriously and we are taking steps to improve general security awareness. Military ID cards form one part of the security measures we have in place. They have photographic ID on them, so it would be difficult for them to be used by individuals they have not been assigned to."
The government has suffered many data-security breaches over the past five months, including the MoD having three laptops stolen containing approximately 600,000 servicemen's and recruits' details, the NHS losing hundreds of thousands of patient records, the Driving Standards Agency losing three million learner drivers' details and HM Revenue & Customs losing 25 million child-benefit details.