Patrick Troughton (Harry Bangate) and Colin Baker (Dr. Dudgeon) both played the Doctor in Doctor Who (1963): Troughton played the Second Doctor from 1966 to 1969 while Baker played the Sixth Doctor from 1984 to 1986.
The book on which this film is based is one of two books that are not a direct part of the 'Swallows & Amazons' series, featuring none of the "Swallows" (the Walker family) or of the "Amazons" (Nancy and Peggy Blackett), for whom the main series is named.