The study will include 300 subjects for screening so that at least 210 will be randomised and a minimum of 168 subjects complete the study/are evaluable. Half the subjects will be on Regimen A in Treatment Period 1and will then be crossed over to Regimen B in Treatment Period 2, and vice versa. Regimen A: BFF (400/12 mcg) by single capsule inhaler. Regimen B: BFF (320/9 mcg) TURBUHALER inhaler. The treatment periods will be separated by a washout Period of 4 weeks.