Rilian wears a mask over his face in this film, a device which does not appear in the novel. This was added to the story to keep the audience from immediately recognizing him, as Richard Henders also plays the part in a flashback earlier in the film.
It is unclear whether the Lady of the Green Kirtle is the same person as the White Witch. She is merely described as "one of the northern witches" (a nod to Lewis and Tolkien's fascination with the Kalevala, the national epic of Finland) However, the actress Barbara Kellerman plays both.
Barbara Kellerman, who plays the Green Lady, previously played the White Witch in The Lion, the Witch, & the Wardrobe (1988). This has led to the popular misconception that the two characters are the same person. In the book, it is merely suggested that the Green Lady is one of the Northern Witches.
There are some scenes unrelated like the dragon appearing at Ruined City of the Giants. At the end of the miniseries, when they emerge from the Underground Kingdom it is summer, during the day. In the book, they emerge into Narnia during the winter, in the middle of a celebration, at night.
Before his death, C.S. Lewis sold the adaptation rights to the entire "Narnia" series. At that time, he absolutely despised television adaptations of his books, believing they were non-realistic, since actors had to wear suits to play non-human characters.
Experiment House satirizes progressive educational institutions such as Summerhill School in England, which were fashionable at the time. CS Lewis also based Jill Pole's experiences of bullying on some of his own. In the book, the head of the school is female.
In the book Prince Rilian was described as not having something quite right about his face. This could have something to do with why Richard Henders - who plays the lost prince in this BBC adaptation - wears a metal head mask that also covers the top part of his face. Incidentally CS Lewis never explained what it was that wasn't quite right about Rilian's face, for example he could have had a frown as his general facial expression. However, it would probably have been hard for Henders to have sustained a frown for a fairly long time, so director Alex Kirby had him wear the mask instead.