Cisco ISE doesn't insert O-N into the Request by default. O-N helps Home sites identify where their users' authentications are coming from. Combined with Chargeable User Identity, Home and Visited sites can provide and follow an audit trail back to a user without the Visited site knowing the users' details.

• Go to Policy → Policy Elements → Dictionaries.
• Open up the System dropdown.
• Open up the Radius dropdown.
• Click on RADIUS Vendors.
• In the RADIUS Vendors Panel click Add and enter
  • Dictionary Name as 'Govroam'
  • Vendor ID as '99999'
• Click on Govroam, then Dictionary Attributes
• Click Add
• Enter:
  • Attribute Name as 'Operator-Name'
  • Data Type as STRING
  • ID as '164'

• Go to Administration → Network Resources → RADIUS Server Sequences.
• Click on which-ever server sequence relates to the Jisc NRPS.
• Click on Advanced Attribute Settings
• Enable Modify Attribute in the request
• Choose Add - Govroam:Operator-Name - 1realm (where realm is your primary realm e.g. 1holby.local)
• Click Save

Note: Due to a bug in ISE I was unable to fully test this. Feedback would be appreciated.