To identify (1) who experiences food insecurity of differing severity and (2) who uses food banks in England, Wales and Northern Ireland; (3) whether the same groups experience food insecurity and use food banks; and (4) to explore country- and region-level differences in food insecurity and food bank use. This pooled cross-sectional study analysed the characteristics of adults experiencing food insecurity of differing severity using generalised ordinal logistic regression models and the characteristics of adults using food banks using logistic regression models, using data from three waves of the Food and You 2 surveys, 2021-2023. England, Wales and Northern Ireland. 18 557 adults. 20·8 % of respondents experienced food insecurity in the past 12 months, and 3·6 % had used a food bank. Food insecurity was associated with income, working status, respondent age, family type, ethnicity, country, long-term health conditions, food hypersensitivity, urban-rural status and area-level deprivation. Severe food insecurity was concentrated among respondents with long-term health conditions and food hypersensitivities. Food bank use was more prevalent among food insecure respondents and unemployed and low-income respondents. Neither outcome showed clear geographical variation. Certain groups experienced an elevated likelihood of food insecurity but did not report correspondingly greater food bank use. Food insecurity is unevenly distributed, and its nutrition and health-related consequences demonstrate that food insecurity will intensify health inequalities. The divergence between the scale of food insecurity and food bank use strengthens calls for adequate policy responses.