The Enfield Poltergeist
The Enfield Poltergeist was a period of apparent poltergeist activity at 284 Green Street, in Enfield, England from 1977 to 1980.
The family involved included a mother, two daughters and two sons. At least 26 of the inexplicable events investigators considered could not be accounted for by fraud. These included moving furniture, flying marbles, interference with bedclothes, cold breezes, pools of water on the floor, apparitions, physical assaults, graffiti, equipment malfunction and failure, disappearance and reappearance of objects, apparent levitations, and fires which spontaneously ignited and extinguished themselves.
A police officer signed an affidavit to affirm that she saw a chair move. One photographer reported being hit on the forehead with a Lego brick.
Among other alleged phenomena they witnessed was [one daughter] speaking using her false vocal folds for hours on end while she was apparently possessed by another entity. Speaking in this way is believed to be medically impossible. When speaking with the false cords Janet said she was “Bill” who had died in the house of a brain haemorrhage.
[Another sister] has stated that although she did fake some phenomena to catch the investigators out, they were not responsible for all the phenomena. She has stated that “It is ridiculous to suggest that either my sister or I could have been responsible for the strange activity that went on in our house.”
[Images from here, which also features a more detailed article and some interesting gifs of objects apparently moving all by themselves. The link also features a documentary on the case called, rather wittily, Interview with a Poltergeist]