This file is a best fit lookup between 2011 middle layer super output areas, electoral wards/divisions and local authority districts in England and Wales as at 31 December 2016. (File Size - 1 MB)
For more information and an overview of best-fitting follow this link - https://geoportal.statistics.gov.uk/datasets/f0aac7ccbfd04cda9eb03e353c613faa/about
REST URL of Feature Access Service – https://services1.arcgis.com/ESMARspQHYMw9BZ9/arcgis/rest/services/MSOA11_WD16_LAD16_EW_LU_65733808e3e940a3969f7c318d9c3022/FeatureServer