The European Monitoring and Evaluation Program Unified Model for the UK (EMEP4UK) simulates the year 2001 to 2014 UK daily average atmospheric composition at a horizontal resolution of 5 x 5 km2. The species included in this dataset are surface daily average concentrations of: nitric oxide (NO), nitrogen dioxide (NO2), particulate matter (PM10 and PM2.5), ammonia (NH3), nitric acid (HNO3), sulphur dioxide (SO2), ammonium (NH4+), nitrate (NO3-), sulphate (SO42-), PM2.5 organic matter, and ground level ozone (O3). The EMEP4UK model framework consists of an atmospheric chemistry transport model (ACTM) which simulates hourly to annual average atmospheric composition and deposition of various pollutants and the weather research and forecast model (WRF). Pollutants simulated include fine particulate matter (PM10, PM2.5), secondary organic aerosols (SOA), elemental carbon (EC), secondary inorganic aerosols (SIA), sulphur dioxide (SO2), ammonia (NH3), nitrogen oxides (NOx), and ground level ozone (O3). Dry and wet deposition of pollutants are also generated by the EMEP4UK. WRF is used to calculate the required meteorological input data for the ACTM. The version of EMEP4UK used to model the 2001-2014 dataset available here is based on the EMEP Meteorological Synthesizing Centre West (MSC-W) model version rv4.4. A more recent version of this dataset, calculated using the EMEP model version rv4.17 and the WRF model version 3.7.1 is available at https://doi.org/10.5285/b0545f67-e47c-4077-bf3c-c5ffcd6b72c8. Notes: Only the simulations for the years between 2002-2012 include data for from forest fire. The emissions used for simulating the years 2013 and 2014 are the same as the year 2012 (updated date will be made available as soon as 2013 and 2014 national emission inventory data have been processed). The calculated year 2001-2012 use a different version of the WRF model, moreover for the year 2013 and 2014 the WRF model setup was changed as the specific Humidity is no longer nudged with re-analysis in the WRF simulation. Acknowledgements required (third-party datasets used to drive the model): The WRF model calculated meteorology uses the dataset from NCEP FNL Operational Model Global Tropospheric Analyses, continuing from July 1999. (http://www.wrf-model.org/). National Centers for Environmental Prediction/National Weather Service/NOAA/U.S. Department of Commerce. 2000, updated daily. NCEP FNL Operational Model Global Tropospheric Analyses, continuing from July 1999. Research Data Archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory. (http://doi.org/10.5065/D6M043C6). Emissions data from the EMEP emissions center (www.emep.int), and NAEI web site (http://naei.defra.gov.uk).