Statins are the most common type of cholesterol-lowering drugs used in clinical practice. Recent research suggests that they may also have anti-inflammatory properties, in particular by inhibition of an important inflammatory cell called a T lymphocyte. Asthma is characterised by chronic inflammation in the airways, which is thought to be regulated by the activity of T lymphocytes. The investigators have found the anti-inflammatory activity of a statin drug in an experimental model of allergic asthma and they have recently shown the beneficial effects of a statin, atorvastatin, in patients with rheumatoid arthritis. These findings demonstrate the therapeutic potential of statin-sensitive pathways in allergic airways disease. The investigators plan to perform a "proof of concept" study to determine the effectiveness of statin therapy in asthma. This randomised controlled trial will test the hypothesis that statins improve asthma control of patients with chronic asthma. The study will be a 22-week randomised controlled trial comparing the effect on asthma control of oral atorvastatin with that of a matched placebo. Each treatment will be administered for 8 weeks separated by a 6-week washout period. A total of 52 allergic asthmatic patients will be recruited to ensure that 44 patients complete the study. The investigators will examine the effect of statin therapy on lung function, symptom scores, exacerbation rates, as well as on the measurement of airway inflammation in sputum and in the blood. This study will determine the benefit of atorvastatin as an add-on therapy in asthma and establish if statins might have a role in asthma management.