From TARDIS Index File, the free Doctor Who reference.

Bedfordshire was an English county. During the 22nd century Dalek invasion, the Daleks established a huge mining facility there as part of their plan to remove the Earth's core and replace it with a power system that will allow the Daleks to pilot the planet anywhere in the universe. Thanks to the Doctor's intervention, the plan failed, and the mines were destroyed in a volcanic eruption. (DW: The Dalek Invasion of Earth)