The Llanfairfach Colliery was a coal mine in the Welsh town of Llanfairfach, located adjacent to Global Chemicals. A year prior to 1973, the mine had been shut down due to competition from the huge corporation and its oil output, and the British government's feelings that coal was a dying industry. However, Global Chemicals saw fit to pump its toxic waste into the heretofore abandoned mine, spawning a horde of giant maggots which threatened the town.
When Brigadier Lethbridge-Stewart (very much against his will) was placed under the command of Global Chemicals director Jocelyn Stevens by the Minister of Ecology, UNIT was ordered to blow up the mine entrance in an effort to trap the maggots underground. Thus it was that the Llanfairfach Colliery was destroyed, however the maggots found an alternate means of getting to the surface.