Participants registered with control practices receive usual care. Primary outcomes are time to first unscheduled contact with acute asthma, and proportion of participants with unscheduled care, assessed from patient records 12 months after recruitment. Secondary outcomes are generic (EQ5D) and disease specific quality of life (AQ20 and North of England scales), prescribing and costs. The trial is powered to detect a 20% reduction in patients attending with unscheduled care (80% power 5% significance). Outcomes will be gathered by blinded researchers. Analysis will be carried out blind to allocation. Cost-effectiveness will be assessed using standard incremental cost-effectiveness ratios.