Migrating the UK’s critical national infrastructure (CNI) from aging analogue networks to modern digital services could deliver a net economic benefit of more than £3 billion by 2040.
A study by Assembly Research, published today by BT, highlights the significant financial, social and environmental benefits of this transition while warning about the rising cost of delay.
Data from the UK telecoms regulator Ofcom reveal that resilience incidents on the Public Switched Telephone Network (PSTN) have increased by 45%, underscoring the growing unreliability of the decades-old system. The analysis identifies a “cost of inaction” of roughly £437 million for CNI customers who postpone migration to digital services.
“This research sends a clear message: delaying the shift to digital carries a real cost to public services, the environment and the wider economy,” said Jon James, CEO of BT Business. “Legacy systems are becoming increasingly unreliable, and the case for action is urgent. BT is committed to guiding the UK’s critical national infrastructure sectors through this upgrade with the resilience and support they need.”
The study examined energy, water, health, emergency services and local government, and it quantifies substantial long-term gains from switching to digital. The energy sector stands to benefit the most, with projected gains of around £1.4 billion driven by improved resilience and more accurate demand forecasting.
The water sector could achieve efficiencies worth approximately £771 million through smarter network monitoring and reduced electricity consumption. Local government could see around £486 million in benefits from modernized telecare systems and lower maintenance costs for obsolete equipment.
Matthew Howett, Founder & CEO of Assembly Research, said: “For the first time, we’ve lifted the lid on legacy network migration and worked to understand the scope and scale of how key UK industries still rely on aging fixed and mobile networks. Our research found that while the energy and water sectors are already well into their migrations, it’s vital that others follow to avoid growing costs and missed efficiencies.”
Beyond the direct economic impact, the transition to digital services promises measurable social and environmental returns. The migration is projected to reduce carbon emissions by 3.42 megatonnes — equivalent to the annual energy use of every home in Birmingham.
Upgrading to modern digital telecare is expected to prevent more than one million emergency call-outs and avoid around 750,000 unnecessary ambulance trips by 2040, averaging over 100 prevented journeys per day.
The shift will also free substantial staff time: an estimated 12 million hours for council employees and more than 600,000 hours for NHS staff, roughly equivalent to the annual workload of 6,500 and 350 full-time staff respectively. Replacing legacy fire alarm systems could also reduce false fire-service call-outs by up to 280,000 incidents.
The UK’s move to full digital connectivity is a major national programme supported by Ofcom and the Government. Although BT migrated nearly 300,000 legacy business lines in 2024, the UK risks lagging behind several international peers. Countries such as Germany and Spain are close to completing their migrations, while Italy, Portugal and France are actively advancing their rollouts.
The PSTN is scheduled for full retirement in January 2027, and organisations across the UK are urged to finish migrations to digital services by the end of 2025 to avoid potential disruption.
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