Inclusion Criteria:  Female of non-childbearing potential or male ≥35 years of age, at the time of signing the informed consent Able and willing to provide informed consent Spirometry-confirmed diagnosis of COPD (FEV1/FVC<0.7 post-bronchodilator) or computerised tomography (CT) proven bronchiectasis Part 1 only: FEV1 ≥50% predicted at screen 1 (i.e. FEV1 prior to any in-clinic administered short acting bronchodilator)  Exclusion Criteria:  Unable to safely use a nebuliser as required by the study according to Investigator's opinion Severe COPD or bronchiectasis defined as FEV1 <20% or requiring non-invasive ventilation History of methaemoglobinaemia Baseline methaemoglobin concentration (using fingertip sensor) > 2% Uncontrolled or severe asthma or history of severe bronchospasm Presence of tracheostomy/inability to provide spirometry or contraindication for performing spirometry Allergy to any of the components of the study intervention Participation in other clinical investigations utilising investigational treatment within the last 30 days / 5 half lives whichever is longer Deemed unlikely to be able to adhere to protocol in view of investigator Any subject who in the opinion of the investigator would not be best served by participating in this clinical trial Any unstable, uncontrolled or severe medical condition which in the opinion of the investigator would make the patient unsuitable for the trial Participant lives at home with no other adults in the household (Part 2 only) On long-term non-invasive ventilation and/or at higher risk of bronchospasm Prescribed Nitric Oxide donating agent (Nitroprusside, Isosorbide dinitrate, Isosorbide mononitrate, Naproxcinod, Molsidomine and Linsidomine) Female of childbearing potential Clinical diagnosis of COPD but Screening Visit spirometry at study centre excludes COPD (i.e. FEV1/FVC post bronchodilator ratio is not <0.7)