To ask the Secretary of State for the Home Department pursuant to the answer of 19 December 2006, Official Report, column 1949W, what the evidential basis is for believing national security could be at risk if an individual is told, on inquiry, whether a personal file exists or not. (113925)

If a terrorist or spy is told the Security Service holds personal data on him or her—so revealing a covert investigation of them—the individual could change their behaviour to thwart that investigation. Alternatively, if told that there is no data held he or she could continue their activities confident in the knowledge that his or her activities had escaped detection. A neither-confirm-nor-deny response avoids both these risks.