OBJECTIVE: To model cost and benefit of a national community health worker workforce. DESIGN: Modelling exercise based on all general practices in England. SETTING: United Kingdom National Health Service Primary Care. PARTICIPANTS: Not applicable. DATA SOURCES: Publicly available data on general practice demographics, population density, household size, salary scales and screening and immunisation uptake. MAIN OUTCOME MEASURES: We estimated numbers of community health workers needed, anticipated workload and likely benefits to patients. RESULTS: Conservative modelling suggests that 110,585 community health workers would be needed to cover the general practice registered population in England, costing £2.22bn annually. Assuming community health workerss could engage with and successfully refer 20% of eligible unscreened or unimmunised individuals, an additional 753,592 cervical cancer screenings, 365,166 breast cancer screenings and 482,924 bowel cancer screenings could be expected within respective review periods. A total of 16,398 additional children annually could receive their MMR1 at 12 months and 24,716 their MMR2 at five years of age. Community health workerss would also provide home-based health promotion and lifestyle support to patients with chronic disease. CONCLUSION: A scaled community health worker workforce integrated into primary care may be a valuable policy alternative. Pilot studies are required to establish feasibility and impact in NHS primary care.