Entry from OED Online

chattering classes (occas. also in sing. chattering class) freq. derogatory, members of the educated metropolitan middle class, esp. those in academic, artistic, or media circles, considered as a social group freely given to the articulate, self-assured expression of (esp. liberal) opinions about society, culture, and current events.
 
  1985 C. JAMES Falling towards Eng. ix. 104 For the English *chattering classes, stories about Australians had begun to serve as a mild form of licensed anti-Semitism, a function they retain. 1990 R. CRICHFIELD Among British vii. 457 The old Britain of Eton, Oxbridge, the land, and the Guards, allied with a chattering class of literary intellectuals, so invaluable when it came to running an empire, is deadly when it comes to bringing the country into the 1990s. 1994 Daily Mail 18 July 8/2 A battle between Middle Englandthe sensible heart of the British middle classesand Islington Person, the politically correct voice of the chattering classes. 1996 Nation 19 Feb. 12/2 You could, like the rest of the chattering classes, obsessively speculate on the emergence of Steve Forbes as Bob Dole's leading challenger. 2000 Sunday Times (Johannesburg) 4 June (Mag.) 6/1 For a day or two, the chattering classes were treated to speculation about government intervention.