In Bentham's theory of institutional design, freedom of the press performs a function analogous to the inspection principle in the Panopticon. Just as visible supervision deters misconduct by officials within an institution, a free press deters misconduct by officials within a government. When legislators and administrators know their actions will be reported, discussed, and criticised, they face a practical incentive to act in the public interest rather than their own. Remove this check and self-serving legislation proliferates unchallenged.
There is also an epistemic dimension to Bentham's case for free expression. Legislation is difficult: it requires accurate information about the likely consequences of proposed rules and the interests of those affected. A government that suppresses inconvenient opinion deprives itself of feedback and operates in a progressively degraded information environment. Freedom of speech is valuable not merely as a check on power but as a source of the knowledge that good legislation requires.
Bentham's defence of press freedom is developed across the Anarchical Fallacies, his later Constitutional Code (1830), and the Essay on Political Tactics (1791), where he advocates full public reporting of parliamentary proceedings.