The broad outline of this is taken from several Joseph Farrell talks and found in some of his books, namely Giza Death Star Destroyed, The Philosopher’s Stone, and Babylon’s Banksters. Ironically, it is also hinted at in David Bradshaw’s Aristotle East and West (Cambridge), though I doubt Bradshaw is aware of the implications. Consider: The last neo-Platonic magician, Iamblichus, died in the 4th century. 500+ years later various occultic movements arise in Europe fully formed and with ideological ties to earlier neo-Platonism. As sociologists of religion are aware, this is simply not how religious movements start. There is an early phase as the group is figuring out its rituals and doctrines, and then a maturer phase. Except these occult groups (think Templars) skipped the earlier phase. The best explanation is that there were underground movements.
Another interesting fact: the ancient Roman senatorial families were suspected of having access to ancient knowledge (from Babylon and Egypt; the latter is easier to prove, since Plato said he took his thoughts from Egypt, and Roman philosophy is a cheap knock-off of Greek philosophy). These senatorial families would later become the Roman curia in the middle ages.
Maybe Colin Gunton is right to hate Gnosticism so much.