TNUoS charges apply to users of Great Britain’s transmission network, recovering the cost of building, operating and maintaining the high-voltage system. Managed by the National Energy System Operator (NESO), the regime ensures users contribute fairly to the cost of transporting electricity nationwide. Because these charges flow through to both generators and end-users, they have wide-reaching implications for the real estate sector, influencing building running costs, supply capacity decisions, and ultimately asset values.

From April 2026, TNUoS enters a new contracted price control period, running until 2031. The contract period, known as RIIO-ET3, is awaiting Ofgem’s final decision due in December 2025. Once confirmed, the contract will determine the revenues allocated to Transmission Owners (TOs) over the period to operate and expand the grid.

What’s changing? 

TOs are urging Ofgem to increase revenue allowances in line with the scale of network expansion required.

That concern is visible in the numbers. NESO’s forecast for total TNUoS revenue in 2026/27 rose from £6.2 billion in April 2025 to £8.9 billion in September 2025, a £2.7 billion increase. Revenues are projected to reach £13.6 billion by 2030/31, driven by inflation, onshore reinforcement, and offshore development.

Generation impact

For generators, RIIO-ET3 brings rising investment needs and shifting tariff dynamics. The contribution from generators is forecast to grow from £1.27 billion to £1.65 billion over the five year price control period, offset by an expansion of the generation charging base from 97.5 GW to 165 GW.

Despite higher overall revenues, the average generation tariff is projected to fall from £13.03/kW in 2026/27 to £10.00/kW in 2030/31, as costs are spread across more assets. Offshore local tariffs will form a growing share of total revenue, reflecting investment in offshore links.

To stay within the €2.50/MWh cap, NESO will maintain a negative adjustment tariff to moderate charges. Together, these trends show a system evolving to fund decarbonisation while preserving fairness and competitiveness for generators.

Demand impact

On the demand side, revenues from charges are forecast to rise from £7.5 billion to £11.8 billion. For households, this equates to an average TNUoS cost of £93.48, or c.10% of an annual electricity bill.

The residual charge, a fixed £/site/day rate from Ofgem’s Targeted Charging Review, ensures cost recovery. The locational element varies across 14 zones, reflecting the cost of supplying power to each region. In 2026/27, the lowest tariffs are expected in Scotland and North East England, while the highest are in London, the South East, and South West, where power must travel further.

These regional differences are likely to persist over the price control period, though future reinforcements may narrow discrepancy.

Real estate impacts

Business owners who lease buildings may seek to reduce their daily fixed charges by reducing their building’s supply capacity. If tenants decrease their supply capacity, the asset value of the occupied building may be negatively impacted.

For building decarbonisation, designers must align electrical load calculations with diversity to avoid allocation into a higher charging band which could assume a significantly higher cost.

NESO will publish the tariff rates for 2026/27 in January 2026. It will be crucial to understand the tariff structure in order to support strategic, long-term decision making.

Further information

Contact Kyle Rarick and Michael Lock