In message , at 07:46:19 on Sun, 25
May 2008, Martin Edwards remarked:
Also it is debatable whether Luton or Stanstead are actually in the
London area. The names are a product of London's self-obsession and
the international obsession with it.

Luton qualifies under your description (even though it's as well
connected to London as Gatwick and arguably better than Stansted) but
Stansted is the official "third London Airport".
--
Roland Perry