The BGS Seabed Sediments 250k dataset is vector data which reflects the distribution of seabed substrate types of the UK and some of its adjacent waters (the UK Exclusive Economic Zone, EEZ) at 1:250,000 scale. This comprehensive dataset provides a digital compilation of the paper maps published by BGS at the same scale, as well as additional re-interpretations from regional geological studies. The seabed is commonly covered by sediments that form a veneer or thicker superficial layer of unconsolidated material above the bedrock. These sediments are classified based on their grain size, which reflects the environment in which they were deposited. This information is important to a range of stakeholders, including marine habitat mappers, marine spatial planners and offshore industries (in particular, the dredging and aggregate industries). This dataset was primarily based on seabed grab samples of the top 0.1 m, combined with cores, dredge samples and sidescan sonar acquired during mapping surveys since the early 1970s. Variations in data density are reflected in the detail of the mapping. The sediment divisions on the map are primarily based on particle size analysis (PSA) of both surface sediment samples and the uppermost sediments taken from shallow cores. Sediments are classified according to the modified Folk triangle classification (Folk, 1954, Journal of Geology, Vol. 62, pp 344–359). The modified Folk diagram and classification used by BGS differs from that created by Folk (1954) in that the boundary between 'no gravel' and 'slightly gravelly' is changed from trace (0.05%) to 1% weight of particles coarser than -1Ø (2mm), shown below. The boundaries between sediment classifications or types are delineated using sample station particle size analyses and descriptions, seafloor topography derived from shallow geophysical and, where available, multibeam bathymetry, backscatter and side-scan sonar profiles. This dataset was produced for use at 1:250 000 scale. These data should not be relied on for local or site-specific geology.