A 7-year-old child with known moderate persistent asthma, currently using a salbutamol inhaler as needed and a regular beclometasone dipropionate (ICS) 100mcg BD inhaler via a spacer, presents with increased daytime symptoms (3-4 times per week) and night-time waking due to cough twice in the last month. His reliever use has increased. What is the most appropriate next step in his asthma management according to BTS/SIGN guidelines?