Background: The NHS Diabetes Prevention Programme (DPP) in England is a behavioural intervention for preventing type 2 diabetes mellitus (T2DM) among people with non-diabetic hyperglycaemia (NDH). How this programme affects inequalities by age, sex, limiting illnesses or disability, ethnicity or deprivation is not known. Methods: We used multinomial and binary logistic regression models to compare whether the population with NDH at different stages of the programme are representative of the population with NDH: stages include (1) prevalence of NDH (using survey data from UK Household Longitudinal Study (n=794) and Health Survey for England (n=1383)); (2) identification in primary care and offer of programme (using administrative data from the National Diabetes Audit (n=1 267 350)) and (3) programme participation (using programme provider records (n=98 024)). Results: Predicted probabilities drawn from the regressions with demographics as each outcome and dataset identifier as predictors showed that younger adults (aged under 40) (4% of the population with NDH (95% CI 2.4% to 6.5%)) and older adults (aged 80 and above) (12% (95% CI 9.5% to 14.2%)) were slightly under-represented among programme participants (2% (95% CI 1.8% to 2.2%) and 8% (95% CI 7.8% to 8.2%) of programme participants, respectively). People living in deprived areas were under-represented in eight sessions (14% (95% CI 13.7% to 14.4%) vs 20% (95% CI 16.4% to 23.6%) in the general population). Ethnic minorities were over-represented among offers (35% (95% CI 35.1% to 35.6%) vs 13% (95% CI 9.1% to 16.4%) in general population), though the proportion dropped at the programme completion stage (19% (95% CI 18.5% to 19.5%)). Conclusion: The DPP has the potential to reduce ethnic inequalities, but may widen socioeconomic, age and limiting illness or disability-related inequalities in T2DM. While ethnic minority groups are over-represented at the identification and offer stages, efforts are required to support completion of the programme. Programme providers should target under-represented groups to ensure equitable access and narrow inequalities in T2DM.