Thanks to reader (and lawyer) Marmion for the reminder!
A common law principle
It is a fundamental tenet of the rule of law that no one is above the law. This principle applies to the government, its officers and instrumentalities: their conduct should be ruled by the law. AV Dicey wrote that the rule of law encompasses:
equality before the law or the equal subjection of all classes to the ordinary law of the land administered by the ordinary Law Courts; the ‘rule of law’ in this sense excludes the idea of any exemption of officials or others from the duty of obedience to the law which governs other citizens or from the jurisdiction of the ordinary tribunals.
In general, the government, and those acting on its behalf, should be subject to the same liabilities, civil and criminal, as any individual.