Also further research in that invaluable ;) resource Wikipedia shows that Zoe Oldenbourg wrote the following book in 1959........

Le Bûcher de Montségur (1959), non-fiction, published in English as Massacre at Montségur: A History of the Albigensian Crusade (translated by Peter Green).

Which gives our Bath Reincarnation females plenty of time to do their homework by 1962 and absorb their 'nightmares' - not that I'm sceptical, and no I did'nt see the programme either....