A 60-year-old male has presented to you in the GP surgery and is complaining of persistent breathlessness, which has gotten worse over time and is worse on exertion. He also has regular sputum production with a productive cough. On examination you notice that there is a wheeze present. He has a pack year history of 30 and worked in the steel works for 25 years before he retired due to his worsening symptoms. What is your main differential diagnosis?