  LONDON Tue Sep 3, 2013 12:07pm EDT  Commuters walk across
London Bridge to the City of London August 7, 2013. REUTERS/Luke
MacGregor   Credit: Reuters/Luke MacGregor  LONDON (Reuters) - A
British exit from the European Union could prompt an exodus of
leading foreign banks and undermine London's dominance of the
foreign exchange markets, the head of the City of London
financial district said in an interview on Tuesday.  Prime
Minister David Cameron has promised to renegotiate the terms of
Britain's EU membership and hold an "in-out" referendum if re-
elected in 2015, prompting fears that the world's sixth largest
economy could drop out of the club it joined in 1973.  The Lord
Mayor of London, whose predecessors have spoken for the
merchants of the City of London since 1189, told Reuters a
possible British exit was a significant threat to London that
would go against 2,000 years of trading history.  "There is a
risk that those foreign exchange desks would move, and that
might apply as much to JP Morgan or Citi