BT has urged the UK's Critical National Infrastructure (CNI) providers to move away from the outdated analog copper landline network by the end of this year.

The telco issued its rallying cry last week, warning that the country's switch from its historic Public Switched Telephone Network (PSTN) is affecting a wide range of critical public systems. BT wants to retire its PSTN network by 2027.

According to BT, this could include water monitoring sensors, phone lines for doctors and pharmacies, fire and burglar alarms, lift alarms, emergency phone lines by roads, help points at train stations, and some older card payment machines.

BT called the transition from analog to digital a "once in a generation" program to future-proof communications for everyone.

The company said it moved close to 300,000 legacy business lines from analog to digital last year. However, the carrier said its data shows many CNI providers are still relying on outdated analog connectivity for mission-critical services.

BT said that as of December, 60 percent of BT CNI customers are yet to formalize a strategy for a transition to digital networks, but did note that noticeable progress had been made by its customers in the energy and water industries.

“With the aging copper landline network becoming increasingly fragile, it’s simply too risky to run the UK’s essential public services on outdated networks," said Bas Burger, CEO of Business at BT. "BT is committed to moving these services onto future-proofed modern connectivity well ahead of the closure of the analog copper network – but we can’t do it alone.

“We're urging all Critical National Infrastructure providers to act now to help protect their services and reap the long-term benefits of going digital. Waiting until the analog switch-off is too late. We’re working with customers to review their technology estate, test their critical devices, and switch to more reliable connectivity by the end of 2025."

Last year, BT Group delayed the shutdown of all copper-based phone lines across the UK until 2027, two years later than originally planned.

BT had initially planned to switch off its Public Switched Telephone Network (PSTN) network by December 2025, but aims to retire the service by January 31, 2027.

The company said that the decision to delay the switch-off aligns with its target of delivering full fiber broadband to 25 million premises by 2026.

In October, the telco revealed it had netted £105 million ($131m) from the sale of its surplus copper cables.

By the 2030s, BT subsidiary Openreach said it expects to "recover up to 200,000 tonnes of copper – in line with customer migrations.”