The two-part stories of the Peter Davison era were almost treated, in budgetary terms, as part of the production of a neighbouring four-part story where the four-part story would be shot predominantly in the studio, while the two-part story enjoyed a larger than usual location shooting allocation. The King's Demons benefits in a big way from the latter, as is evidenced by the opening scenes.
It's rare to see a medieval period piece with a full cast in Doctor Who, but the opening joust sequence is actually quite remarkable. There are a healthy number of extras, and there's some great action scenes during the joust itself. Another characteristic of the Davison two-part stories was that they often were handed to young directors or directors new to Doctor Who. Tony Virgo directs his only two episodes of Doctor Who with The King's Demons, but his work is impressive. There's one shot that I particularly enjoy in this episode. It's when Hugh is knocked off his horse. He falls into shot, quite close to the camera, and lies there grimacing while, in the background and out of focus, Sir Gilles Estram dismounts his horse, discards his shield, takes his sword from his squire, and advances on Hugh to finish the job. And all of that happens in one uninterrupted camera shot. I will always be impressed by good quality camera work.
Once the story retreats into the studio, the effect is no less impressive as the scenes set in the great hall look lavish, accompanied by lute players and jesters. There's also a mystery behind why King John has been seen in two places at the same time on this day, 4 March 1215. It's almost a shame that The Master materializes at the end of the episode (again, why was he disguised?) because it had been a great little unassuming episode up until then.