Houston had a successful career as a character actor in British film and television, with prominent parts in several well-known films, including Yangtse Incident (1957), The Longest Day (1962, in which he appeared alongside Richard Burton), 633 Squadron (1964), Where Eagles Dare (1968, again with Burton) and The Sea Wolves (1981). He would sometimes indulge his Welsh accent, and at other times conceal it behind an English public school voice. His forte tended to be authority figures, often military, such as the brilliant but tough David Caulder, the head of Moonbase 3, or Dr Francis in "Thirteen to Centaurus" (from the anthology series Out of the Unknown).