Past emission controls in the UK have substantially reduced precursor emissions of health-hazardous fine particles (PM_2.5) and nitrogen pollution detrimental to ecosystems. Still, 79% of the UK exceeds the World Health Organization (WHO) guideline for annual mean PM_2.5 of 5 μg m^-3 and there is no enforcement of controls on agricultural sources of ammonia (NH₃). NH₃ is a phytotoxin and an increasingly large contributor to PM_2.5 and nitrogen deposited to sensitive habitats. Here we use emissions projections, the GEOS-Chem model, high-resolution datasets, and contemporary relationships between exposure and risk of harm to assess the potential human and ecosystem health co-benefits in 2030 relative to the present day of adopting legally required or best available emission control measures. We estimate that present-day annual adult premature mortality attributable to exposure to PM_2.5 is 48,625, that harmful amounts of reactive nitrogen deposit to almost all (95%) sensitive habitat areas, and that 75% of ambient NH₃ exceeds levels safe for bryophytes. Legal measures decrease the extent of the UK above the WHO guideline to 58% and avoid 6,800 premature deaths by 2030. This improves with best available measures to 36% of the UK and 13,300 avoided deaths. Both legal and best available measures are insufficient at reducing the extent of damage of nitrogen pollution to sensitive habitats, as most nitrogen emitted in the UK is exported offshore. Far more ambitious reductions in nitrogen emissions (>80%) than is achievable with best available measures (34%) are required to halve excess nitrogen deposition to sensitive habitats.