Strange lights and shadowy figures have been spotted in the building in the evening and at weekends.

ECONOMIST: A working model?

They include accounts of strange lights in the sky and unexplained objects being spotted by the public, armed forces and police officers.

BBC: Files released on UFO sightings

Some think airmen sent it up as a joke to add some 'evidence' of a craft to the sightings of strange lights.

BBC: Rendlesham Forest UFO mystery still leaves questions

If he is right, an earthquake will generate enormous electrical currents in the ground precisely the sort of thing that would upset the ionosphere and generate strange lights in the form of lightning-related phenomena.

ECONOMIST: Predicting earthquakes