This is behind the FT paywall so if you have a sub it might be worth a read
http://www.ft.com/cms/s/6e7d100a-2641-11e6-8ba3-cdd781d02d89,Authorised=false.html?siteedition=uk&_i_location=http%3A%2F%2Fwww.ft.com%2Fcms%2Fs%2F0%2F6e7d100a-2641-11e6-8ba3-cdd781d02d89.html%3Fsiteedition%3Duk&_i_referer=&classification=conditional_standard&iab=barrier-app#axzz4AKiNpyKa
