Eric Thompson didn't understand French, and never read any translation of the original story lines.
For budgetary reasons, on The Magic Roundabout television series, Eric Thompson provided the voices for ALL the characters. In this spin-off feature film he decided to not voice the character of the Blue Queen and instead gave the role to actress Fenella Fielding as he wanted that character to have it's own distinctive voice to echo it's own mysterious and sinister personality.
Footage of Dougal boarding the train from the early part of the film, is seen on a television in the film Stardust (1974).
No known film prints of the English language version of the film could by found for years as it had come and gone from cinemas after its 1972 UK release and had been shown on TV a couple of times around 1977/78. It was then forgotten about until an English language print was found in the latter half of the 1980s and released on home video in 1989.