There is concern regarding the impact that a global infectious disease pandemic might have, especially the economic impact in the current financial climate. However, preparedness planning concentrates more upon population health and maintaining a functioning health sector than on the wider economic impact. We developed a single country Computable General Equilibrium model to estimate the economic impact of pandemic influenza (PI) and associated policies. While the context for this development was the United Kingdom, there are lessons to be drawn for application of this methodology, as well as indicative results, to other contexts. Disease scenarios were constructed from an epidemiological model which estimated case fatality rates (mild, moderate and severe) as 0.06%, 0.18% and 0.35%. A clinical attack rate of 35% was also used to produce influenza scenarios, together with preparedness policies, including antivirals and school closure, and the possible prophylactic absence of workers. U.K. cost estimates (in Sterling) are presented, together with relative percentage impacts applicable to similar large economies. Percentage/cost estimates suggest PI would reduce GDP by 0.3% (£ 3.5 bn), 0.4% (£ 5 bn) and 0.6% (£ 7.4 bn) respectively for the three disease scenarios. However, the impact of PI itself is smaller than disease mitigation policies: combining school closure with prophylactic absenteeism yields percentage/cost effects of 1.1% (£ 14.7 bn), 1.3% (£ 16.3 bn) and 1.4% (£ 18.5 bn) respectively for the three scenarios. Sensitivity analysis shows little variability with changes in disease parameters but notable changes with variations in school closure and prophylactic absenteeism. The most severe sensitivity scenario results in a 2.9% (£ 37.4 bn), 3.2% (£ 41.4 bn) and 3.7% (£ 47.5 bn) loss to GDP respectively for the three scenarios.