Shortly after the third series of "Van der Valk", Foster took on the role of Sherlock Holmes in a series of radio plays in 1978. He recorded 13 episodes of the Holmes canon, with David Buck as Dr Watson. Foster was seen on BBC television in "Fall of Eagles" (1974, in the role of Kaiser Wilhelm II and as the condescending chief of British Intelligence in the adaptation of the John le Carré novel "Smiley's People" (1982). During this time, Foster appeared in the films "Sweeney!" (1977), spun off from the TV series; "The Wild Geese" (1978); Merchant Ivory's "Heat and Dust" (1983); "The Whistle Blower" (1986); and "Maurice" (1987).