Like several others here, I, too decided to rewatch "Pyramids of Mars". My media was the 2004 DVD edition. I played the story with the audio commentary by director Paddy Russell, producer Philip Hinchcliffe and actors Liz Sladen and Michael Sheard. I know the story itself almost by heart, but I had forgotten a lot of "behind the scenes" details from the cast and crew.
I noted upthread how Sarah revealed considerable skills with firearms, well, at least rifles. Apparently, that was fully director Russell's doing. We heard both her POV and Ms. Sladen's. Liz wanted to play it as being a tad wary of the firearm, being as much surprised that she hit the gel-ignite (dynamite to us bloody Yanks) as she was that the explosion was being contained. Russell disagreed and insisted Sladen play the scene with unwavering confidence. Thing was, Liz was not familiar with guns and didn't expect the "crack" of the gun powder to be as loud as it was. She stated she went deaf for a few minutes after firing the blank.
Sladen also stated that she caught the flu adter recording this story. While bright and clear, it was winter and she didn't consider wearing thick enough underwear to compensate for the frilly, almost sheer dress. She also explained the dress originally had a high collar, but she found blouses, shirts and sweaters with such to be almost clausterphobic, so they modified the gown for her comfort.
Michael Sheard (Lawrence Scarman) confessed he "nicked" the photo that supposedly depicted the Scarman brothers as children) and still had it at the time they recorded the commentary.
While not present for the commentary, there was a supplementary video interviewing others associated with the production including Bernard Archard (Marcus Scarman) and Peter Copley (Prof. Warlock). Despite both being the oldest among the cast, Sladen, Sheard and Hinchcliffe all hinted the elder thespians seemed to be the more impish among the actors with Archard confessing having to "stay after 'school'" with Russell wanting to "have a word" with him. Archard himself stated the same in the separate interview clip. He did seem to have a gleeful twinkle in his eyes, far, far different for the baleful glare of the possessed Scarman. (Of course, that's his skill, he's an actor.)