Inclusion Criteria:  Adult patients with a clinically confirmed diagnosis of eCRS by a ENT undergoing maximal medical therapy as part of their standard of care. Having undergone functional endoscopic sinus surgery at least 6 months prior to enrolment. Participants with an endoscopic bilateral nasal polyp score of ≤5 out of a maximum score of 8 Score > 2 on disease severity visual analogue scale (VAS) A minimum body weight >=40 kilograms (kg) at screening visit Gender: Male or female (females of childbearing potential must use adequate birth control methods and not plan to get pregnant during the course of the study). Informed consent: Willingness to give written informed consent and willingness to participate to and comply with the study. Age ≥18 but <80 years.  Exclusion Criteria:  Subjects with known hypersensitivity or contraindications to Betamethasone Dipropionate, corticosteroids or topical anaesthesia. Subjects with sino-nasal abnormalities, disease or implanted devices that prevent application of the therapy. Previous enrolment in this study. Subjects currently required systemic corticosteroid use or receiving biologic therapy as part of their disease management plan or who meet the PBS criteria for severe lower airway disease. Subjects with history or current glaucoma or cataract or if they have abnormal IOP at screening or pre-treatment (abnormal IOP is defined as greater than 21 mm Hg). Subjects with other conditions that could lead to elevated eosinophils such as Hypereosinophilic Syndromes, including Churg-Strauss Syndrome, or Eosinophilic Esophagitis. Subjects with acute sinusitis. Subjects with known immunodeficiency. Subjects with Diabetes (Type 1). Subjects with cystic fibrosis. Pregnant subjects or subjects currently lactating as the effect on human pregnancy is unknown.