ArcGIS Enterprise version 10.5.1 and above
Within your ArcGIS Enterprise portal add a new item pointing at the REST endpoint URL for the relevant service. A full list of the URLs can be found below.
In the content section choose to add a new item from the web. Enter the URL and when prompted enter your ArcGIS Online credentials. Choose to store the credentials with the item. This will create an item where the authentication is performed for you every time it is accessed, without the need for you to enter the credentials yourself. This item can now we shared as normal.
GB Premium Basemap Classic https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/BaseMap_OS_VML_MasterMap/MapServer
OS Premium Rasters Basemap https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/Basemap_OS_Premium_Rasters/MapServer
OS MasterMap Basemap https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/BaseMap_OS_MasterMap/MapServer
OS VectorMap Local https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/BaseMap_OS_VectorMap_Local/MapServer
OS 25K Raster https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/Basemap_OS_25K/MapServer
OS 50K Raster https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/Basemap_OS_50K/MapServer
OS VML Colour Raster https://tiles.arcgis.com/tiles/qHLhLQrcvEnxjtPr/arcgis/rest/services/Basemap_OS_VML_Colour_Raster/MapServer
GB Pavement Width Indicator https://services.arcgis.com/qHLhLQrcvEnxjtPr/arcgis/rest/services/GB_Pavement_Widths/FeatureServer
OS MasterMap Buildings https://services.arcgis.com/qHLhLQrcvEnxjtPr/arcgis/rest/services/OS_MasterMap_Buildings/FeatureServer
TitleInfo https://services.arcgis.com/qHLhLQrcvEnxjtPr/arcgis/rest/services/TitleInfo_v2/FeatureServer
GB Premium Basemap
Similar to the above, an item referencing the underlying Vector Tile Service item can be created in your ArcGIS Enterprise portal, however additional steps are required to create the accompanying styles. A Python notebook is available to automate this process, creating the proxy item, retrieving all available styles, updating them to reference the proxy, and sharing them to a group within your organisation.
ArcGIS Enterprise prior to version 10.5.1
You will need to follow the pattern for making the item a public item in ArcGIS Online and then adding the internal portal URL as one of the allowed URLs in “Limit Usage”.