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.