I ve bronceictasis and mild asthma, do I need 2 use inhalor. Ie;seretide regularly to keep chest free from mucus? Or only should take it when breathless

Regular use. Seretide is meant to be a controller medication that should be used on a daily basis. It will not be effective for immediate relief of acute symptoms and should not be used as a rescue inhaler when you are acutely ill. Please discuss an action plan with your doctor so you know which medicines to use daily & which ones are to be used when you are having acute symptoms.
Maybe. Seretide is a combination of inhaled steroid with long-acting bronchodilator used for the treatment of moderate to severe persistent asthma. Mild persistent asthma does not typically require this combination, but still requires regular treatment with usually an inhaled steroid. A quick relief bronchodilator is used as needed for symptoms. The real question is why is there bronchiectasis?