Electricity transmission network spending is expected to rise nearly fourfold from ~£18bn across RIIO-ET2 (FY 2021-25) to ~£70bn across RIIO-ET3 (FY 2026-31). Transmission Network Use of System (TNUoS) revenue is expected to nearly double from ~£5.1bn in 2025-26 to ~£8.9bn in 2026-27, and forecasts are also rising for Distribution Use of System (DUoS) costs with RIIO-ED3 in April 2028.
Understanding and preparing for these charges has never been more important for developers and generators.
Here are five developments to be aware of that will impact network charges in the coming years
1. The ET3 framework governs a period where large transmission investments are expected to support Clean Power 2030 goals. To account for changes in future demands and costs, ET3 includes uncertainty mechanisms and re-openers so that allowances can be adjusted in-period.
2. Ofgem has committed to reforming TNUoS—alongside connection charging and other transmission charging arrangements—with the aim of delivering new charging arrangements by 2029 at the latest.
3. Ofgem’s initial ED3 framework emphasises a shift toward longer-term, strategic planning and proactive anticipatory investment. This tends to increase upfront expenditure allowances compared with the mostly reactive approach in ED2.
4. The DUoS Significant Code Review (SCR) has been de-prioritised, and Ofgem is now awaiting clearer context from broader market design work (REMA, TNUoS reform and Energy Cost Allocation and Recovery review) before progressing further.
5. Strategic Energy Planning (SEP) being delivered by NESO will see GB move toward a more coordinated, system-wide planning of generation, networks, storage and demand, and will determine what gets built and when, and who pays for it.
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Unlock the Exclusive BlogWith cost volatility, steep rises, and reforms to charging arrangements delayed it can be challenging to navigate the unknown and a changing cost landscape. Our market expertise, forecast and analysis, can ensure your decisions are evidence-based.
Cornwall Insight's Network Charging Forecast tool provides expert long-term projections of TNUoS and DUoS charges across all GB zones and technology types. Our forecasts enable developers to stress-test investment cases against different charge scenarios, support portfolio analysis for multi-asset investors, and provide the granular locational intelligence needed for site selection. As part of the service, we also assess key drivers such as regulatory modifications and changes to the generation mix.
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