On the stairs up to the first time they enter, Mainwaring is holding the candelabra with the shorter candles and Frazer is holding one with longer candles. As they enter the room the reverse is true.
When PIke is naked up the tree, in one shot you can see that the actor is wearing a coat.
For most of the episode the only light is supposed to come from hand-held candles and at one point a flickering fire. There are no artificial lights, yet the light level is far too bright for such illumination and the shadows don't move when the people carrying the candles walk about.