Hi Cris,
Yes, you can use CER in the UK :)
KEY BENEFITS
Cisco Emergency Responder enhances the E9-1-1 functionality inherent in Cisco CallManager, and creates an unrivaled "Dynamic E9-1-1" solution for organizations with multi-line telephone systems:
• Meets and exceeds traditional E9-1-1 features
• Automates all user and phone moves, adds, and changes
• Enables users and phones to move an unlimited number of times per day
• Avoids the expense and burden of daily PS-ALI record uploads
• Avoids daily documentation updates that potentially introduce errors
• Enables quicker and more effective emergency response from onsite personnel and public agencies
• Provides configuration auditing to facilitate responsible change management and investigative or legal processes
• Provides call history logs for capacity planning, management of emergency call abuse, and incident documentation
•*** Is compatible with any emergency number (for example, 999 in UK, E1-1-2 across Europe)
https://www.cisco.com/en/US/prod/collateral/voicesw/ps6789/ps7046/ps842/product_data_sheet09186a008009253a.html
Hope this helps!
Rob
