The National Security Act 2023 is an Act of the Parliament of the United Kingdom. It introduced measures intended to strengthen national security against espionage, interference in the political system, sabotage and assassination.

The Act’s core measures came into force on 20 December 2023. It repealed and replaced the Official Secrets Acts of 1911, 1920 and 1939.

The law is relevant to the government’s stated efforts to strengthen its powers against foreign threats. Its existence does not, by itself, establish that a foreign actor interfered in a particular election or referendum.