Martial law

Martial law was a state of government in which military leaders took power. The Marshal of Solos took power under martial law after the death of the Administrator. (TV: The Mutants)

Brazen placed the human colony on Frontios under martial law after the disappearance of Plantagenet. (TV: Frontios)

In the aftermath of the spaceship crash in the Thames and the disappearance of the Prime Minister of the United Kingdom in March 2006, General Asquith threatened to impose martial law when Acting Prime Minister Joseph Green, along with Oliver Charles and Margaret Blaine, didn't take the events seriously. The reason for their strange behaviour was discovered when they revealed themselves to be members of the Slitheen family before killing Asquith. (TV: Aliens of London)

In Pete's World, London was placed under martial law after the Cybermen moved into the city and the EarPods were activated. (TV: The Age of Steel)