When Last We Left our Hero...
I love it when the strip itself recaps everything for you!
The American distributor, Lippert Pictures, insisted on name-value US actors as leads to help sell the British films to theatres.
Otherwise they wouldn't put money into the projects.
(When Hammer made a new US distribution deal with Warner Brothers in 1957, the casting requirement was dropped.)
BTW, I had mentioned yesterday that the original mini-series was six half-hour episodes.
They were, in fact, forty minutes each, with no commercials, for a total running time of four hours, which makes the compressing of the whole story into under ninety minutes in this film even more remarkable!