Gardner said he was initiated in September 1939, near Christchurch in the New Forest, into a coven that was the surviving remnant of an old pagan religion of witchcraft. Everything he published afterwards was framed as the disclosure of an inherited tradition rather than the founding of a new one.
No independent evidence of that coven has ever been produced. Ronald Hutton's The Triumph of the Moon (1999), the standard scholarly history, concluded that Wicca cannot be traced to an unbroken pagan survival, and that its actual sources are identifiable and recent: Margaret Murray's theory of an organised witch-cult behind the early modern trials, which professional historians had already discredited; ceremonial magic, above all Crowley and the Golden Dawn; Leland's Aradia; folklore; and Gardner's own reading in Freemasonry and the East. Philip Heselton, the most sympathetic and most thorough of his biographers, worked the same evidence and arrived at a coven that, if it existed, had itself been assembled in the mid-1930s by people who had read Murray, which is a defence of Gardner's honesty rather than of his tradition's antiquity.
The test case is Dorothy Clutterbuck, the woman Gardner named as his initiator. It was long suspected he had invented her. Doreen Valiente settled that in 1985 by obtaining her birth, marriage and death certificates: Clutterbuck was entirely real. What has not been shown is that she was a witch. She never described herself as one, was a practising Anglican, and Hutton found no occult connection; Heselton, arguing from her surviving diaries and their nature-mystical tone, contends she was a pagan in all but name. That is a live disagreement over the same documents rather than a settled question, and the weight of academic opinion sits with Hutton.
The honest summary is the one Hutton himself insists on, and it is not deflationary: Wicca is not an ancient survival, it is the first new religion England has produced in modern times, and it has spread worldwide. Being new is not the same as being fraudulent. What is fraudulent is the claim of antiquity, and Gardner made it.