Setting your 999 emergency address — Ofcom CESID compliance for VoIP

A traditional landline has a physical address baked into it — if you call 999 from a BT copper line, the emergency operator sees the address the line is installed at. SIP and VoIP don't. The trunk runs over the internet and can be physically anywhere — your office, your home, a coffee shop. So the 999 operator relies on the address you (the business) registered with your carrier.

Setting that address correctly is the most important five-minute job in your first week. If you call 999 from the office and the system shows the operator the registered-office address in Birmingham instead of the actual factory in Bristol, you've got a problem.

What Ofcom requires

Under Ofcom General Conditions A3, every UK telecom provider must offer access to 999/112 emergency services from every number they allocate. As part of that, providers must collect a location address for every fixed-location number — known in industry as the CESID(Calling Emergency Service ID) or simply "emergency address".

When you call 999 from a UK SIP/VoIP service:

• The call routes from your trunk to the UK emergency network
• The CESID associated with the calling number is presented to the operator
• The operator dispatches emergency services to that address
• Battenberg arrives. (Or doesn't, if the address is wrong.)

What address to set

• The physical location where the phone will actually be used— not your registered office, not your accountant's address, not your home if the phone lives at the office
• Full postal address including building name/number, road, town, postcode
• For larger sites, add the floor / suite so emergency services can navigate quickly inside the building

Multiple sites or remote workers

If your business operates from multiple physical locations, set a separate CESID per trunk corresponding to where the phones at that trunk actually are:

• One trunk per office is the cleanest setup. Each trunk gets the office address as CESID.
• SIP-trunked remote workers — for a sales rep working from home, the home address should be the CESID for the number they use. This is a known awkward area of SIP — the address travels with the registration, not the phone.
• Softphone users moving around — there isn't a clean answer to this in current Ofcom guidance. The registered CESID is the address dispatched to. Train users to give their actual location verbally when they call 999 — the operator always asks.

How to set or change your CESID

You don't set this yourself — we manage emergency addresses for you so they're always validated against the official format before they reach the emergency database. Tell us the address and we'll register it:

• Email help@numbergroup.com or call 0800 310 1010 with the number (or trunk) and the full address — building name/number, street, town, county, postcode
• We set the Emergency Address (CESID) against that trunk and confirm back to you
• You can see your registered numbers and current details any time in the read-only customer portal — but changes go through us so nothing reaches the 999 database mis-formatted

Updates propagate to the UK emergency database within 24 hours. If you've just moved and need a faster update, tell us when you contact us — we can expedite.

How to test

Don't dial 999 to test. Emergency operators don't appreciate test calls and you can be fined.

Two safe ways to validate:

• Ring our team and ask us to confirm the CESID record we've stored for your trunks — we'll read it back to you verbally
• Some emergency authorities (e.g. BT Operator Assistance) run validation services on request — ask our team if you want this arranged for a critical site (call centres, healthcare, sites with vulnerable users)

When to update it

• Office move
• New office opened
• Trunk re-purposed for a different location
• Permanent shift to home working — update to the home address of the user who has that trunk

Other 999/112 compliance basics

• Don't block 999 in your PBX's outbound dialling restrictions. Even if you block all UK and international, 999/112 must remain dialable.
• Don't require an access digit (9) before 999. A lot of PBXs do — a user under duress dials 999 directly and the call fails. Configure 999/112 to bypass any access-digit requirement.
• Train staff to give their location verbally when calling 999. Even with correct CESID, the operator always asks. Best practice: post a small sign by the phone with the building's exact address.
• Battery-backed phones— if your business relies on phones working during a power cut, plan for it (UPS, PoE-with-battery switches). The PSTN switch-off removed the traditional "phone still works in a power cut" assumption many users had.

Why this matters

In 2018 a UK SME had a heart-attack incident at their factory. The phone system had a default CESID set to the accountant's address from a setup form filled in years earlier. Ambulance went there first. The patient survived but lost ~10 minutes — meaningful in a cardiac event.

It's a 5-minute job to get this right on day one. Tell us your address before you do anything else.