The section featuring the Museum is from around 30 minutes into the programme. It is worth sticking with it to the end for the part which says "Quite simply you've sold your soul!" and then a shot of the Museum interior back then.
The youtube description: An extremely rare documentary about Witchcraft aired once in the UK in 1971. Featuring contributions from Eleanor Bone, Cecil Williamson, Alex & Maxine Sanders, Doreen Valiente et al. Very much of its time and with some very rare footage, also includes reference to the famously unsolved murder of Charles Walton on Meon Hill.