 Methods The investigators will perform a randomised, cross-over, open label trial of bisoprolol versus celiprolol with 10 people who have moderate to severe COPD. The study will last between 10-12 weeks for each person. Potential participants will be recruited from our existing database of volunteers with COPD, contacted either by telephone, email or post and invited to participate. Those invited will receive a written patient information document detailing the requirements of the study and the extent of their participation before attending for a screening visit. Participants will be given at least 24hours to read the information document before deciding whether or not they agree to be screened. The study will include 5 visits to the department including the screening visit for the various tests outlined below. Each visit may last for around 3 hours. If participants agree to coming along for a screening visit, they will be asked to withhold any long-acting bronchodilators for 48hours and short acting bronchodilators for 6 hours as is standard practice when confirming the diagnosis of airway obstruction COPD using clinical pulmonary function measurements. 