Ever since John Grierson popularized the term ''documentary,'' British non-fiction film has been renowned, sometimes reviled, but seldom properly appreciated. ''100 British Documentaries ''provides a uniquely accessible, occasionally provocative introduction to a rich and surprisingly varied tradition by considering 100 examples taken from across a century''s worth of output. The 100 films range from the Victorian period to the present day. Alongside such classics as ''Night Mail ''and ''Touching the Void ''are documentaries that illustrate the many uses to which it has been put from pro-gram-filler to political propaganda to classroom teaching aid and the many styles and viewpoints it has embraced. While the focus is on the documentary ''film,'' several television productions are included, indicating how the genre has developed on the small screen.
