Greece, unable to form a coalition government will go back to the polls in a month. Widely predicted to win is the socialists who are pledged to withdraw Greece from The E.U. and the Euro. If that happens banknotes may be overprinted but the transition back to the Drachma could be slower similar to the British decimalisation in the 70's. Speculation on that is rife but a more reliable source is that from Reuters that De La Rue is making plans to print the new currency. Could be a good time for banknote collectors who get in early. http://www.huffingtonpost.co.uk/2012/05/18/greek-crisis-british-money-drachma_n_1526903.html?ref=uk
