MI5 has ways of blocking secret files release

Individuals have the right under the Data Protection Act 1998 to request access to files and information public sector bodies may hold on them. But the Act provides the likes of MI5 with a number of exemptions that can be invoked. If it is in regards to national security, concerns can be challenged in the courts and MI5 can also use a certificate signed by the home secretary to prove an exemption is required.