From Wikipedia:
Neil John McCallum (1929–1976) was a British-Canadian actor. After attending the Guildhall School of Music and Drama in London, McCallum's first major appearance on stage was alongside Sam Wanamaker in The Rainmaker in the mid-1950s.[3] He appeared in British TV series in the 1950s, 1960s and early 1970s, including The Saint, Department S and UFO, and in films such as The Siege of Pinchgut (1959) and Dr. Terror's House of Horrors...
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The Lost Continent
As First Officer Hemmings
Moon Zero Two
As Space Captain
Dr. Terror's House of Horrors
As Jim Dawson
Hazard
As Syd
The Siege of Pinchgut
As Johnny Kirk
The Inspector
As Browne
Catacombs
As Richard 'Dick' Corbett
The War Lover
As Sully
The Scent of Fear
As Karl Schling
The Devil's Disciple
As Christie Dudgeon
The Longest Day
As Canadian Doctor (uncredited)
Walk a Tightrope
As Counsel
Thunderbirds Are GO
As Dr. Ray Pierce (voice)
Foxhole in Cairo
As Sandy
Quest for Love
As Jimmy
Jet Storm
As Gilbert
Department S
As Eddie Curtis
The Protectors
As Bennett
UFO
As Carl Mason
Jason King
The Saint
As Nick Vashetti
No Hiding Place
The Expert
As Cooper
Sir Francis Drake
As Sir Martin
International Detective
As Chet Lawton
Maigret
Space School