A population viability analysis of the North Norfolk Sandwich tern (Sterna sandvicensis) population was undertaken by Centrica Renewables at the request of Natural England, to understand potential impacts of estimated collision at Centrica’s Docking Shoal and Race Bank proposed offshore wind farms in the Greater Wash, with a third consented site, Sheringham Shoal (SCIRA) included in background mortality. The model developed specifically for the purpose, ViaPop, is an individual-based model with the potential to understand the relative effects of different population parameters (ie sensitivity analysis) at greater depth and sophistication than an off-the-shelf package. Population parameters were determined directly from the data on the relatively well-studied north Norfolk colonies coupled with estimates of some parameters from the literature, with estimates of survival rate determined by a specific analysis of British Trust for Ornithology ring recovery data. A project board of experts in the field approved the use of the different parameters used in ViaPop. The analysis was presented as suplementary information to the environmental statement.