From 1 April 2026, Transmission Network Use of System (TNUoS) charges are set to increase significantly across Great Britain. Even if a business has fixed electricity unit rates, this change could still lead to higher overall electricity costs.
The National Energy System Operator (NESO) has now published the confirmed tariffs for the 2026/27 charging year, with industry analysis pointing to an average rise of around 60–64% compared with 2025/26 levels. While the exact impact varies by site and contract structure, this marks one of the most substantial movements in transmission-related charges in recent years.
For energy managers, procurement teams and financial controllers, this development highlights the increasing importance of non‑commodity costs within electricity bills and the need to understand how these costs flow through supply contracts.
What Are TNUoS Charges?
TNUoS charges fund the operation, maintenance and expansion of the high‑voltage electricity transmission network across Great Britain.
This network moves power from large‑scale generators to regional distribution grids and major demand centres. Every year, NESO sets new tariffs for the charging year (1 April–31 March), and suppliers pass these costs through to end‑users—either built into the unit rate or as a separate line item.
The framework governing how TNUoS is calculated is regulated by Ofgem.
How TNUoS Costs Appear in Supply Contracts
Businesses typically encounter TNUoS in one of two ways:
- All‑Inclusive Pricing
TNUoS charges are built into the unit rate.
The supplier takes on pricing risk but may factor cost forecasts into the offer.
- Pass‑Through Pricing
TNUoS is billed as a separate third‑party charge.
Here, increases apply directly during the contract term as tariffs change.
Both models are common, but they offer different levels of predictability. During years with large network‑charge movements, the difference becomes critical.
What’s Changing From April 2026?
Final TNUoS tariffs for 2026/27 were released on 30 January 2026. Industry commentary indicates a 60–64% average increase year-on-year.
However, this uplift is not uniform. The impact at site level depends on:
- geographic region
- demand banding or meter profile
- connection voltage
- demand patterns
- how the contract treats third‑party charges
As a result, some sites may see modest increases, while others could experience much higher uplifts.
Why Bills May Rise Even When Wholesale Prices Fall
Electricity bills are broadly split into two parts:
- Commodity costs – the wholesale electricity price
- Non‑commodity costs – network charges, balancing charges, policy costs, metering, etc.
Public debate often focuses on wholesale markets. However, for many organisations, non‑commodity charges now make up a substantial share of the bill. This means that even if wholesale prices soften, network charge increases—such as the April 2026 TNUoS uplift—can still push total costs higher.
Non‑Commodity Costs and the Energy Transition
Energy transition and grid‑modernisation costs rarely appear as a simple “net zero charge”. Instead, they’re embedded across multiple cost elements, including:
- transmission and distribution charges
- system-balancing services
- policy mechanisms
- infrastructure upgrades supporting the shift to low‑carbon generation
TNUoS is not an environmental levy, but it does recover the cost of expanding and adapting the transmission system, which is increasingly shaped by changes in where and how power is generated.
NESO’s long‑term revenue forecasts suggest that transmission costs will continue rising in the years ahead.
Other System Charges to Be Aware Of
In addition to TNUoS, businesses may encounter charges like:
BSUoS – Balancing Services Use of System
Covers the real‑time costs of balancing supply and demand on the transmission system.
These charges are regulated by Ofgem and apply across the market. Suppliers differ only in:
- how they forecast charges
- how transparently they present them
- how they reconcile changes during the contract
Who Will Be Most Affected in April 2026?
The businesses most exposed include:
Pass‑Through Contract Customers
TNUoS increases will likely flow through directly from April 2026.
Businesses Renewing in Q1–Q2 2026
Updated network‑charge forecasts may already be baked into supplier pricing.
Multi‑Site Organisations
Contract structures may vary by site, creating inconsistent cost exposure across a portfolio.
Where TNUoS Appears on Your Bill
Depending on your supplier, TNUoS may appear within:
- the unit rate
- standing charges
- third‑party charge sections
Some suppliers convert standing‑charge elements into a £/MWh equivalent for comparison purposes. This can make rising costs more visible—even if consumption is unchanged.
Practical Steps Businesses Can Take
- Review Your Contract Structure
Understand whether your contract is all‑inclusive or pass‑through, and which charges can change during the term.
- Consider Renewal Timing
If your renewal falls near April 2026, ensure all quotes reflect the impact of the new charging year.
- Compare Quotes on a Like‑for‑Like Basis
Key elements to examine:
- treatment of third‑party charges
- supplier forecasting assumptions
- standing charge structure
- reconciliation processes
- Reduce Avoidable Consumption
Even if network charges can’t be avoided, usage can be. Focus on:
- out‑of‑hours consumption
- unnecessary baseload increases
- operational peaks
- site inefficiencies
Frequently Asked Questions
When do the new TNUoS charges take effect?
From 1 April 2026, for the 2026/27 charging year.
Will all businesses see a 60–64% increase?
No. This is a national average. Actual impact varies widely.
Can switching supplier avoid TNUoS charges?
No. TNUoS is a regulated market-wide charge. Suppliers differ only in how they structure or present it.
Are energy transition costs included in bills?
Yes—through multiple network and system charges rather than one single line item.