4: The Multiplex. During the late seventies and early eighties, British cinemas witnessed a dramatic fall in audiences, blamed on shabby interiors, the popularity of television and a lack of good blockbuster films. In 1985 an American I idea-themulitplex-wasbroughtto Milton Keynes. Forbes examines its design and popularity. Producers Sara Jane Hall and Julia Reming Fordetailssee Monday (R)