Fire Trap

From Tardis Wiki, the free Doctor Who reference

On Christmas Day, 2006, the Sycorax came to Earth in the Fire Trap. It was later destroyed by the Torchwood on the command order of Harriet Jones. (DW: The Christmas Invasion)

Though the exact size of the ship was unknown, it was large enough to cast a huge shadow over London.

Behind the scenes

According to the non-narrative based work REF: Doctor Who: The Visual Dictionary, Fire Trap was the name of the asteroid on which the Sycorax originated. It was located in the JX82 system and was composed mainly of rock and ice, with very little in the way of natural resources such as metals. The tribes lived just below the surface of the asteroid. When an unidentified spaceship collided with the asteroid, the Sycorax stole the engines of the ship and fitted them within the asteroid, using it as a spaceship.