Should you wish to create your own basemaps you can use the same tiling schema as the EsriUK Maps+ services. To do this download it from AGOL (links are below) and use it when publishing your service.
BNG Vector Tiling Schema: https://esriukcontent.maps.arcgis.com/home/item.html?id=83c5498758b349b8886b057d7857b49d
BNG Raster Tiling Schema: https://esriukcontent.maps.arcgis.com/home/item.html?id=6e811b785a18408bb8fdb31fe5c1f5ee