Randles specializes in writing books on UFO and paranormal phenomena. To date 50 of these have been published, ranging from her first UFOs: A British Viewpoint (1979) to Breaking the Time Barrier: The race to build the first time machine (2005). Subjects covered include crop circles, ESP, life after death, time anomalies and spontaneous human combustion.

According to her publishers, Simon & Schuster, Randles studied physics and geology at university, has written articles for New Scientist, and has sold more than 1.5 million copies of her fifty published books. It was stated in 1997 that her books had been published in 24 countries.

The same source states that she was the story consultant to the ITV TV series Strange But True? that ran between 1993 and 1997, and that she has also done documentary work for the BBC.

Randles is a regular contributor to the magazines Fortean Times and The Skeptic and has spoken at the UnConvention.

She was editor of Northern UFO News (a 12-20 page A5 journal detailing UFO activity within Northern England) from 1974 up to 2001.

"Oz Factor" is a term invented by Randles in 1983 to describe the strange, seemingly Altered state of consciousness commonly claimed by some witnesses of unidentified flying objects and other similar paranormal events. Randles has noted the strange calmness and lack of panic described by the witnesses, relative to the bizarre circumstances that they described and says that they described and defined the Oz factor as "the sensation of being isolated, or transported from the real world into a different environmental framework...where reality is but slightly different, [as in] the fairy tale land of Oz." Oz Factor She has further noted that "[t]he Oz factor certainly points to consciousness as the focal point of the UFO encounter."

Among Randles' numerous published books are the following:

• The UFOs That Never Were, co-written with Andy J. Roberts and Dr. David Clarke (ISBN 1902809351) Reviewed
• UFO Retrievals: The Recovery of Alien Spacecraft (ISBN 0713724935)
• Breaking the Time Barrier: The Race to Build the First Time Machine
• Time Storms: The Amazing Evidence of Time Warps, Space Rifts and Time Travel
• Supernatural Pennines
• Spontaneous Human Combustion
• Beyond Explanation
• U.F.O. Conspiracy: From the Official Case Files of the World's Leading-Nations
• UFOs and How to See Them
• The Unexplained: Great Mysteries of the 20th Century
• Supernatural Isle of Man 2003 Robert Hale LTD ISBN 0-7090-7076-4
• The UFO Conspiracy: The First Forty Years
• The Paranormal Year
• Psychic Detectives
• Men in Black: Investigating the Truth Behind the Phenomenon
• Time Travel: Fact, Fiction and Possibility
• The Afterlife: An Investigation into the Mysteries of Life After Death
• Science and the UFOs
• Complete Book of UFOs, The: Investigation into Alien Contacts and Encounters
• Alien Contact : Window on Another World, co-written with Paul Whetnall, 1981
• UFO Study- updated (2007) edition can be found on Northern UFO News website (see below):