Protecting National Security by Breaking the Law? Prerogative, Statute and the Powers of MI5

Abstract

The Court of Appeal decision in Privacy International v Foreign Secretary (2021) found lawful the long‐secret policy governing the purported authorisation and commission of criminal offences as part of the work of MI5 and its informants. The Court found MI5 had a public law power to engage in such criminality, historically under the royal prerogative and more latterly as an implied power under the Security Service Act 1989. The authors argue that these findings threaten serious damage to core constitutional principles, including the rule of law and settled understandings of the prerogative and its relationship with statute. They postulate a much narrower implied legal power under the 1989 Act, authorising only the making of representations to the CPS on whether it would be in the public interest to prosecute. This would provide a narrow path for MI5 officers and their informants to avoid legal jeopardy for activities core to its mission.