Any entity that wishes to use NSG data will need to agree to terms and conditions of supply set out in a "click through" page for registered users. This can be found on the NSG data download section of the NSG website managed by GeoPlace(TM) LLP.
One of the main conditions of supply of NSG data is that the user must also be appropriately licensed for the use of certain underlying Ordnance Survey data before GeoPlace is able to allow access to the NSG data.
This briefing note provides a short summary explaining the requirement for users of NSG data to be licensed for the use of underlying Ordnance Survey data. The briefing note can be seen at http://www.ordnancesurvey.co.uk/docs/papers/use-of-nsg-and-ordnance-survey-data.pdf