By definition, we don’t know what is suppressed by governments; who knows, maybe there are aliens at Roswell, Presley is alive and well and Nixon shot Kennedy. However, unofficial leaks as well as official reclassifications of secret data always excite interest, so it seems reasonable to assume that there is some information that remains classified with good reason. However old information such as military ciphers, designs for armaments and discussions that suggests more than usual levels of incompetence of mendacity among the political classes, they are likely to remain secret – for the excellent reason that confidence in the entire system depends on it. For better or worse, that process tends to be called national security.