In January 2027, the UK’s Public Switched Telephone Network (PSTN) will be permanently switched off, bringing an end to the copper-based analogue phone network that has quietly underpinned the nation’s connectivity for decades. While it might sound like a routine telecoms upgrade, the implications are far-reaching. The PSTN still supports thousands of essential services across the UK – from phone lines and lift alarms to fire systems, telecare devices, and personal alarms – many of which play a critical role in real-time operations across healthcare, energy, logistics, emergency response, and other vital sectors.

For the UK’s Critical National Infrastructure (CNI) sectors, this is not just a technical change. It represents a moment of reckoning. These organizations rely on reliable, always-on connectivity to deliver essential public services. And while the switch-off date may seem distant, waiting until 2027 to act could be a serious mistake. Because when it comes to safeguarding national resilience, last-minute transitions are simply too risky.

The digital engine behind CNI

Modern CNI operations don’t just rely on internal systems – they are increasingly dependent on cloud services hosted in large-scale data centers. These digital infrastructure hubs power everything from patient records and dispatch systems to smart grid management, traffic controls, and real-time diagnostics. In many ways, data centers have become the digital engine rooms of the UK economy and public service ecosystem.

But even the most advanced data center cannot operate in isolation. Its effectiveness hinges on the strength of the connection between the data center applications and the people, systems, and devices accessing it. If hospitals, utility control centers, or emergency service networks are still running on legacy PSTN lines and the legacy broadband that operates across the old telephone circuits, they face an increasing risk of outages or outright failure. That’s a serious concern in sectors where even a few seconds of disruption can have life-threatening consequences.

Time for an upgrade

The copper PSTN network, first introduced in the Victorian era, was never built for the realities of today’s digital world. The PSTN was installed in the early 80s, and early broadband was introduced using the same lines in the early 90s. And the truth is, it needs to retire, having operated past its maintainable life span.

Modern work depends on real-time connectivity and data-heavy applications, with expectations around speed, scalability, and reliability that outpace the capabilities of legacy infrastructure.

But technical limitations aren’t the only reason the copper PSTN is being retired. The network is increasingly prone to outages, service degradation, and performance bottlenecks – risks that are particularly serious for those who depend on it for essential services. With replacement parts becoming harder to source and maintenance growing more complex, the case for a modern upgrade is not just compelling, it’s urgent.

In contrast, fiber is built for high-speed, high-capacity communication. It can transmit vast volumes of data in real time, support stable cloud-based applications, recover quickly from outages, and provide a secure, scalable foundation for distributed operations. Crucially, it also supports the level of resilience CNI sectors require.

But this transition takes time. Shifting from copper to fiber-based, all-IP infrastructure is far from an overnight fix. It demands detailed planning, rigorous system testing, migration of legacy devices, and close coordination with technology partners. Crucially, redundancy should also be built in from the outset. It’s not enough to replace ageing infrastructure; CNI organizations should ensure that new networks incorporate failover systems, dual routing, and automatic switchover capabilities. These redundant paths are vital for maintaining service continuity during outages or disruptions, particularly in high-stakes scenarios where digital systems come under intense pressure.

Fiber-based all-IP networks are engineered to support this level of resilience, enabling critical operations to continue without interruption even in adverse conditions. All of which reinforces the risk of delay and the need for urgency. Postponing migration only increases the likelihood of a last-minute scramble as the 2027 switch-off draws near.

The case for action now

That’s why BT is encouraging CNI sectors to complete their transition planning and ordering by the end of 2025 – 13 months ahead of the formal PSTN closure. Planned migration allows time for thorough audits of dependent systems, validation of new solutions, and robust risk mitigation strategies, plus time for ordering, installing, and testing.

CNI organizations that act now can identify and replace vulnerable PSTN-connected systems, including alarms, monitoring equipment, and legacy comms, to ensure compatibility with modern data center-hosted platforms, so that no single point of failure puts critical operations at risk. It will also help avoid pressure on suppliers and service providers who will face peak demand as the 2027 deadline nears.

But the benefits extend beyond risk mitigation. Early adopters gain access to improved service delivery, greater operational agility, enhanced cybersecurity, and the ability to scale digital transformation projects with confidence.

The bigger picture: enabling national resilience

CNI sectors aren’t just consumers of connectivity; they’re the backbone of national resilience. Whether it’s a GP retrieving patient records or an energy network adjusting supply in real time, their operations depend on uninterrupted, high-integrity access to cloud systems and data center infrastructure.

That’s why the PSTN switch-off must be seen not as a Telecoms milestone, but as a strategic resilience imperative. Without universal access upgrades, even the most advanced data centers can’t fulfil their role. The priority now is to build a truly modern digital backbone. One that gives homes, businesses, and CNI facilities alike robust, high-speed connectivity into the cloud.

This is about more than retiring copper. It’s about enabling a smarter, safer, more responsive nation. Organizations that move early won’t just minimize risk, they’ll unlock new levels of agility, performance, and digital assurance.

The cloud is ready. Data centers are ready. And the new networks are ready.

As a provider of critical services, are you ready? Let’s build the backbone of a more resilient nation.