Britain’s National Energy System Operator (NESO) keeps the lights on across the GB power grid. Until this year, it was doing part of that job by fax.
The detail sits, in plain language, inside an Ofgem Grid Code decision from March 2025. That decision, filed as GC0175, quietly deleted the words “fax” and “facsimile” from six sections of the Grid Code. The background note Ofgem attached is the interesting part:
“The NESO currently use fax machines within the Control Centre to send and receive data from Primary and some Secondary Balancing Mechanism Units (BMUs). A number of these data submissions from BMUs support critical functions such as System Restoration, by transmitting data such as Unit Availability.”
BMUs are the power stations, batteries, and storage units the control room calls on to balance supply and demand second by second. System Restoration is what gets the lights back on after a blackout. Unit Availability tells the control room which generators can actually respond right now. Not the sort of thing you would expect to arrive on a curl of thermal paper.
Why fax survived this long inside a national grid operator is a familiar answer for anyone who has watched regulated industries cling to proven tools. It worked, it was auditable, and every counterparty was already set up on it. NESO’s own explanation cites the practical version: “hardware support contracts ending (or have ended) and replacement parts difficult to source.” Replacing it required a public code amendment, a unanimous recommendation from the Grid Code Review Panel, and Ofgem sign-off. Not a routine IT swap.
The forcing function is not a change of heart. It is BT. The Public Switched Telephone Network that fax rides on is scheduled to shut down by the start of 2027, and every non-voice service on it goes with it. The replacement, per Ofgem, is “an Azure-based Designated Information Exchange System” that is expected to preserve “the stability and audit trail that the current fax solution provides.” NESO is not leaving fax because fax was bad. It is leaving because BT is turning off the line.
A related Ofgem report, a different story
A separate Ofgem decision this March suspended the Frequency Risk and Control Report for 2026, the annual document that sets out how NESO manages the frequency risks behind the 9 August 2019 outage that affected more than one million customers. Some coverage has bundled the two events into a single fax narrative. The primary decision letter tells a duller cause. Ofgem rejected the FRCR 2025 in December, ordered a rewrite due 31 March 2026, and NESO could not then produce a fresh six-month report by 1 April. Ofgem’s own note on the suspension: “no material impact on system risks.”
The genuinely interesting story is still the fax one. A national grid operator was routing System Restoration signals over a technology being retired by the phone company. If your work ever lands you a fax number from a regulated institution, now you know the institutional logic behind it. Sometimes the answer is to pay per fax once and move on.