Overview

In order to access these services you must be in possession of a national licence for the data from the OS which covers the relevant datasets

The GB Premium Basemap Classic is designed to be used as background mapping providing a seamless map view from small to large scales with a consistent cartographic representation. 

The sources of data are Ordnance Survey Vector Map District data for small and mid-scales, and Vector Map Local & MasterMap for the largest scales. For currency of this data, please see the release notes here: Release Notes – Help | Maps+ (esriuk.com)

The coverage of the map service is GB. 

The map projection is British National Grid. 
The map service is cached down to 1:500, but can be viewed at an additional level of detail at 1:250 scale.