Objective: To estimate the impact and equity of existing and potential UK salt reduction policies on primary prevention of cardiovascular disease (CVD) and gastric cancer (GCa) in England. Design: A microsimulation study of a close-to-reality synthetic population. In the first period, 2003–2015, we compared the impact of current policy against a counterfactual ‘no intervention’ scenario, which assumed salt consumption persisted at 2003 levels. For 2016–2030, we assumed additional legislative policies could achieve a steeper salt decline and we compared this against the counterfactual scenario that the downward trend in salt consumption observed between 2001 and 2011 would continue up to 2030. Setting: Synthetic population with similar characteristics to the non-institutionalised population of England. Participants: Synthetic individuals with traits informed by the Health Survey for England. Main measure: CVD and GCa cases and deaths prevented or postponed, stratified by fifths of socioeconomic status using the Index of Multiple Deprivation. Results: Since 2003, current salt policies have prevented or postponed ∼52,000 CVD cases (IQR: 34,000–76,000) and 10,000 CVD deaths (IQR: 3000–17,000). In addition, the current policies have prevented ∼5000 new cases of GCa (IQR: 2000–7000) resulting in about 2000 fewer deaths (IQR: 0–4000). This policy did not reduce socioeconomic inequalities in CVD, and likely increased inequalities in GCa. Additional legislative policies from 2016 could further prevent or postpone ∼19,000 CVD cases (IQR: 8000–30,000) and 3600 deaths by 2030 (IQR: −400–8100) and may reduce inequalities. Similarly for GCa, 1200 cases (IQR: −200–3000) and 700 deaths (IQR: −900–2300) could be prevented or postponed with a neutral impact on inequalities. Conclusions: Current salt reduction policies are powerfully effective in reducing the CVD and GCa burdens overall but fail to reduce the inequalities involved. Additional structural policies could achieve further, more equitable health benefits.