Complex sentence: Key left at the end of 1985 and was replaced by Norman Cook--the future Fatboy Slim--and drummer Chris Lang was replaced by Hugh Whitaker, former drummer with The Gargoyles, who in turn was replaced with Dave Hemingway.
Split into simpler sentences: Key left at the end of 1985 and was replaced by Norman Cook (the future Fatboy Slim). Drummer Chris Lang was replaced by Hugh Whitaker, former drummer with The Gargoyles, who in turn was replaced with Dave Hemingway.