Martial law was a state of government in which military leaders took power.
After dinosaurs began appearing in central London as a result of Operation Golden Age, the area was evacuated and martial law instigated. The military ordered that all looters who failed to surrender were to be shot. (TV: Invasion of the Dinosaurs)
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 R. Asquith threatened to impose martial law when Acting Prime Minister Jocrassa Fel-Fotch Passameer-Day Slitheen, disguised as Joseph Green, along with his other family disguised as government officials, didn't take the events seriously. (TV: Aliens of London)
During the Martian Civil War, Grand Marshall Raxlyr placed New Mars under martial law. (AUDIO: The Prisoner of Peladon)
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)