National Grid files £4.5bn re-opener request with Ofgem for transmission upgrades

The request, filed through Ofgem's re-opener process, covers transmission enhancements, new low-carbon generation connections, heavy industrial demand support, and resilience investment. Re-openers allow network operators to seek funding beyond what was agreed at the start of a regulatory period when system requirements change materially. National Grid has argued that rising connections from renewables, large industrial users, and data centres have created precisely those conditions.

The proposals are anchored to the RIIO-T3 agreement, which sets the baseline transmission investment framework for the upcoming regulatory period. National Grid's broader capital programme allocates £70 billion across its UK and US networks over the next five years, and this £4.5 billion request represents a material acceleration of the UK portion. Ofgem will now consult on the proposals before issuing a funding determination.

What this means for UK commercial energy buyers

UK day-ahead baseload power over the past year provides the wholesale backdrop against which any TNUoS-driven movement in non-commodity costs will land for commercial buyers.

Transmission investment approved through re-openers ultimately flows through Transmission Network Use of System (TNUoS) charges, which form part of every commercial electricity contract's non-commodity cost stack. A decision to approve the full £4.5 billion would place upward pressure on TNUoS tariffs, though the timing and magnitude of any pass-through depends on Ofgem's phasing of the allowances and how National Grid structures delivery.

Buyers most exposed to this decision include:

• High-consumption industrial and manufacturing sites with demand-led TNUoS exposure
• Multi-site portfolios where non-commodity costs already represent a significant share of the bill
• Organisations procuring on fully fixed contracts that embed current TNUoS forecasts
• Data centre operators and EV fleet managers whose connection timelines depend on the funded upgrades
• Buyers with renewables power purchase agreements (PPAs) where grid connection delays affect contracted volumes

For context, TNUoS charges for large industrial and commercial (I&C) demand consumers already run to several pounds per megawatt hour depending on triad zone and consumption profile. Any step-change in the approved allowance base would be reflected in future tariff years, not immediately.

Ofgem's review timeline has not yet been confirmed, but re-opener determinations of this scale typically involve a formal consultation period of several months before a final decision. The outcome will shape how quickly National Grid can progress connection queues, which National Grid ESO has separately flagged as a key bottleneck to Britain's clean energy build-out. Buyers renewing contracts for periods extending into 2027 and beyond should monitor the consultation outcome and factor potential TNUoS movement into their procurement strategy.