The target enrollment is 1800 randomised subjects at approximately 200 study centers globally. The total duration of subject participation will be approximately 27 weeks, consisting of a 2-week run-in period, 24-week treatment period and a 1-week follow-up period. Subjects will run-in on their existing COPD medications for 2 weeks and in addition will be provided with short acting albuterol/salbutamol to be used on an as-needed basis (rescue medication) throughout the study. Subjects will discontinue all existing COPD medications during the randomised treatment period but may continue their study supplied rescue albuterol/salbutamol. A sub-set of approximately 400 subjects will remain on blinded study treatment for up to a total of 52 weeks to provide additional long term safety data.