This dataset contains fuel moisture contents and flammability metrics for samples of common heather (Calluna vulgaris) collected across the United Kingdom between 15th April and 20th May 2023. A total of 830 samples were used to measure fuel moisture content (FMC), and 130 of these were also subjected to calorimetric analysis. FMC data were obtained gravimetrically by weighing samples before and after drying. Flammability data were obtained by micro-scale combustion calorimetry, which measures heat release related to flaming combustion of a fuel material. The flammability metrics recorded were the heat release capacity (HRC), peak heat release rate (PHRR), total heat release (THR), and temperature at maximum rate of decomposition (Tmax). These data will contribute to the development of models of fuel moisture variability in UK fuels, and thus refine inputs for fire behaviour modelling, which can inform land management strategies in relation to wildfire risk. Full details about this dataset can be found at https://doi.org/10.5285/64d340d7-8f19-49f9-90e0-83d4013e76c2