if I interpret this correctly (British) copyright expired in 2000 as Stapledon died in 1950.
"In the 1911 Act the term of author's copyright was extended to the lifetime of the author and 50 years thereafter; this remained the case under the 1956 Act and the 1988 Act.
The 1911 Act in effect extended the meaning of "author" so that this period of copyright applied to all types of works, not merely printed works.
Under the 1995 Regulations (set out below), the period of author's copyright was further extended, to the lifetime of the author and 70 years thereafter."
http://en.wikipedia.org/wiki/Copyright_law_of_the_United_Kin...
"In the 1911 Act the term of author's copyright was extended to the lifetime of the author and 50 years thereafter; this remained the case under the 1956 Act and the 1988 Act. The 1911 Act in effect extended the meaning of "author" so that this period of copyright applied to all types of works, not merely printed works. Under the 1995 Regulations (set out below), the period of author's copyright was further extended, to the lifetime of the author and 70 years thereafter." http://en.wikipedia.org/wiki/Copyright_law_of_the_United_Kin...