 The study design incorporates a proportion of participants already established on Mepolizumab as well as participants who will be commenced on Mepolizumab on entry to the study. A baseline assessment of medical history, clinical examination, lung function and sputumbloodurine for analysis will be undertaken along with quality of life questionnaires. Those newly started on Mepolizumab, will be assessed in a similar manner 3 months into the study. 