Charles Cardell was involved in Witchcraft at the same time as Gardner. He claimed to have been initiated as a 'Wiccen' by his mother and seems to have been involved with a group whose practices revolved around a God named 'Atho' though the picture is more complex than I suggest here. Initially Cardell appears to have been quite friendly with Gardner, but over the years animosity between them grew.
Cardell believed that Gardner was hoaxing the nation and had created a Witchcarft based on his personal proclivities and misapproprtiated the use of the Egptian flail, soemthing that Cardell held sacred.
In 1964, shortly after Gerald's death, Cardell, under the pseudonymn 'Rex Nemorensis', published much of the Gardnerian Book of Shadows in a small booklet entitled 'WITCH'. The information is thought to have come into Cardell's hands via a woman called Olive Green (A.K.A. Olwen Armstrong Maddocks), who had received an initiation and the Book of Shadows from Gerald in the late 1950s. Alternatively, Cardell may have acquired the material himself as there is one piece of evidence that asserts that Gardner had initiated Cardell in the late 1950s. A mutual exchange of material would have been in keeping with both Gardner's and Cardell's characters.
You can read my 2007 article about Charles Cardell, Raymond Howard and the Head of Atho. But in 2021 I embarked on new research and my book on the Coven of Atho should be appearing in early 2022.
A recent article about some original Coven of Atho papers, along with a few images of them, held at the Norfold Record Office can be read here
For more information about Charles Cardell please check out his entry on my Other 1950s Witches page.
Watch a video about The Coven of Atho:
Cardell at the entrance to Dumblecott
A video compilation about Charles and Mary Cardell