Affable, gentlemanly British character actor of long stage experience who began making regular appearances in British and American films beginning in the late 1940s. Among his more than 50 credits are "The Happiest Days of Your Life" (1950), "Mogambo" (1953), "Lust for Life" (1956), "The Singer Not the Song" (1960), "The Trials of Oscar Wilde" (1960), "Cleopatra" (1963) and "Deadlier Than the Male" (1967). In the 60s, Naismith concentrated on theater, doing "Here's Love" and "A Time for Singing" on Broadway, and "The Apple Cart" and the 1970 revival of "The Winslow Boy." He is probably best remembered by contemporary audiences for his whimsical Merlin in Joshua Logan's film of "Camelot" (1967) and for encouraging Roger Moore and Tony Curtis to accept dangerous assignments each week in the tongue-in-cheek TV adventure series "The Persuaders."