This is a best fit lookup between 2011 Output Areas (OA) and counties/unitary authorities as at 31 December 2018 in England. (File Size - 18 MB)Field Names - OA11CD, CTYUA18CD, CTYUA18NMField Types - Text, Text, TextField Lengths - 9, 9, 28REST URL of Feature Access Service – https://services1.arcgis.com/ESMARspQHYMw9BZ9/arcgis/rest/services/OA11_CTYUA18_EN_LU_58828e4c97234e60b45f92bb75af1ddb/FeatureServer
For more information and an overview of best-fitting follow this link - https://geoportal.statistics.gov.uk/datasets/f0aac7ccbfd04cda9eb03e353c613faa/about