In August 1977, strange things started to happen in a quiet north London suburb. This unusual, terrifying activity lasted several months and became known as the Enfield Poltergeist. Among those who witnessed this apparently paranormal activity were journalists and the police. Some of the evidence is controversial. But 30 years on it remains the best-documented and most puzzling case of its kind, and may be the first time that a spirit voice has been captured on tape.

• Richard Dillane