Summary

  • The UK’s updated CNI charter separates provider, network-operator and asset-owner duties, but leaves CNI identification partly to the organisations that rely on the old lines.
  • A signature is not a continuity receipt: readers need circuit-level inventories, tested devices, power boundaries and documented escalation before a copper connection is withdrawn.

A line that rings in an office may also feed a pump alarm, a control dialler or a building system whose owner is several contracts away from the network operator. The UK’s telecoms modernisation puts those less visible dependencies under pressure as analogue PSTN and ISDN services give way to digital connections. The question raised by the government’s updated Critical National Infrastructure (CNI) charter is practical: who can prove that a particular essential service still works after its line changes?

The charter, updated on 13 October, asks communications providers to identify CNI customers with whom they have a direct relationship, accept self-identification and find CNI circuits where possible. Providers must offer a dedicated contact, help customers identify legacy-network use, work with equipment makers on tests and alternatives, and pursue senior-level engagement before a non-consensual move. If a customer does not engage, the provider must alert the Department for Science, Innovation and Technology (DSIT) and allow government escalation first. DSIT says it will establish a process with clear timelines. These are voluntary commitments, not a published tally of circuits already found or equipment already passed in testing. The CNI charter

Its scope is narrower than the phrase “critical infrastructure” can suggest. The charter specifically covers PSTN or ISDN assets and services where losing connectivity could cause death or casualties, including functions in defence, health, transport, water and electricity. It encourages wider use for all qualifying CNI, but does not set an exhaustive asset list. A routine line at a hospital is not automatically a critical circuit; a service outside a named CNI sector might still meet the government’s impact test. Asset owners are expected to tell their provider which use cases they consider critical.

That makes classification a shared process, and it makes silence or incomplete inventories an operational risk rather than a clerical gap.

The responsibilities also stop at different points in the supply chain. Communications providers sign up to all six commitments. Network operators and wholesalers, which may lack a direct relationship with the end customer, commit to equipment testing and to the notice and escalation steps in clauses three to five. The charter places devices and services not supplied by a provider with the CNI asset manager, equipment vendors and manufacturers.

A provider may help a customer identify a dialler; that does not establish that the dialler’s supplier has tested it on the replacement service or that the end-to-end alarm path reaches its receiving centre.

Power is another boundary to record. When asked, the provider must explain network resilience during an outage and discuss options. The charter says the provider manages network resilience, while the CNI customer supplies power to the devices it relies on. A powered core network can therefore coexist with a silent alarm if its local modem, gateway or connected device loses power. The relevant evidence is a complete service test under the power conditions the customer expects to face, including any transition product, battery limit and restoration procedure—not a general claim that “the network is resilient.”

The time window is narrowing. Parliament reported 3.6 million PSTN lines still operating at the end of 2025, down from 6.5 million a year earlier; that national total says nothing about how many critical CNI circuits remain. The government’s timeline says Openreach PSTN users are due to migrate by 31 January 2027, with 108 exchange closures beginning by 2030. Those dates are schedule evidence, not proof of local readiness. The parliamentary statement · The connectivity timeline

The practical benchmark is therefore a record for each critical service: a named owner and provider, the underlying circuit and any upstream dependency, the function carried, an agreed replacement, an equipment test with a pass criterion, power and failover limits, and a dated escalation outcome where engagement fails. The existing non-voluntary migration checklist and final engagement protocols describe safeguards for customers who do not respond, but they do not substitute for a service-specific result. The non-voluntary migration checklist · The provider engagement protocol · The network-operator and wholesaler protocol The broader fixed-network charter sets wider notice and communication commitments, but its public page does not report CNI circuit test results. Fixed telecoms modernisation charter