The Transmission Network Use of System (TNUoS) charge is one of the less visible parts of an electricity bill, but it’s becoming increasingly important. Over the next 12–18 months, updates to how these charges are calculated and recovered are expected, with most suppliers forecasting notable increases from April 2026.
This short update explains what TNUoS is, what’s driving the change, and how CUB is approaching it when advising clients on upcoming renewals.
What is TNUoS?
TNUoS (Transmission Network Use of System) is the mechanism used by the National Energy System Operator (NESO) to recover the cost of maintaining and operating Great Britain’s high-voltage transmission network — the pylons, substations and circuits that move electricity across the country.
Suppliers pay these charges to NESO and recover them from customers through standing charges or other non-energy components on electricity bills.
The amount depends on:
- where in the country the supply is located (each region has a tariff zone),
- how much electricity is used and when it’s used, and
- whether the meter is half-hourly (HH) or non-half-hourly (NHH).
NESO issues draft TNUoS tariffs in November and final tariffs by the end of January for implementation from 1 April each year.
What’s changing
NESO’s latest five-year forecasts, and analysis from across the energy industry, point to higher TNUoS charges from April 2026 onwards.
The main drivers are:
- Major investment to reinforce and expand the national transmission network, particularly to connect renewable and offshore generation.
- New price control allowances (RIIO-ET3), which let network operators recover higher costs through TNUoS.
- Adjustments to locational and residual charging, shifting more recovery into fixed standing-charge elements.
- Ongoing methodology reforms which may change how sites are banded and billed.
While the scale of increase will vary by region and voltage level, most forecasters expect standing charges to rise significantly from 2026/27.
Final published tariffs are due in early 2026, so there remains some uncertainty until those figures are confirmed.
What this means for renewals and tenders
Because TNUoS is set centrally and applies to all suppliers, each will take a slightly different approach to managing the risk of these increases.
Some build a forecast into their fixed rates, others treat TNUoS as a pass-through cost that moves when NESO updates its tariffs.
Until the final TNUoS costs are published, it would be misleading to describe any electricity product as entirely “fully fixed”.
At CUB, we take a cautious approach: we flag the uncertainty early, explain how each offer handles non-energy costs, and outline which products are more or less exposed should the final charges rise above forecast.
CUB’s position
We believe transparency is essential.
Our role is to make sure you understand the differences between supplier terms — whether an offer provides broader cover, partial protection, or passes through all future TNUoS adjustments — so you can make an informed choice that suits your level of risk tolerance.
We’ll continue to monitor NESO and Ofgem publications and update you as new information becomes available.
Key dates to note
- November 2025 – NESO publishes draft TNUoS tariffs for the 2026/27 year
- January/February 2026 – final tariffs confirmed for implementation
- 1 April 2026 – revised tariffs come into force, with methodology changes expected to begin applying
References / further reading
- NESO: TNUoS charges overview – https://www.neso.energy/industry-information/charging/tnuos-charges
- NESO: Charging documentation hub (charging statements, guidance, policy) – https://www.neso.energy/industry-information/charging/charging-documentation
- NESO: Statement of Use of System Charges (Charging Statement 2025/26, PDF) – https://www.neso.energy/document/362701/download
- NESO: Five-Year View / Webinar deck (TNUoS tariff timetable and forecasts, PDF) –
https://www.neso.energy/document/318596/download - NESO: Five-Year View of 2026/27 to 2030/31 TNUoS tariffs (dates and milestones, PDF) – https://www.neso.energy/document/353071/download
- Ofgem: CMP444 cap-and-floor updates for wider generation TNUoS charges – https://www.ofgem.gov.uk/publications/authority-update-decision-timing-cmp444-introducing-cap-and-floor-wider-generation-tnuos-charges
- Drax Energy Insights: TNUoS standing-charge increases in 2026/27 – https://energy.drax.com/insights/tnuos-tariffs-forecast-to-grow-significantly-in-2026-27/
- Drax Energy Insights: NESO TNUoS Five Year Review – https://energy.drax.com/insights/neso-tnuos-5-year-view/
