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

National Grid's re-opener applications cover transmission enhancements, new connections for low-carbon generation, support for heavy industrial demand, and resilience improvements across the network. The re-opener process allows network operators to seek supplementary funding when system requirements move beyond what the original price control settlement anticipated. At £4.5 billion, this is a material addition on top of the RIIO-T3 baseline that Ofgem and National Grid agreed for the current regulatory period.

The driver is a convergence of demand signals that was not fully priced into earlier planning. Renewable generation projects, large industrial users, and data centres are all queuing for grid connections at a rate the existing network cannot absorb. National Grid has stated that the portfolio was shaped through whole-system analysis, asset health assessments, and an evaluation of delivery methods, positioning this as a costed, structured ask rather than an open-ended funding request. The £4.5 billion sits within the company's broader five-year £70 billion capital programme across its UK and US networks.

What this means for UK commercial energy buyers

UK day-ahead power across the last 12 months sets the wholesale baseline against which any TNUoS uplift would land on commercial buyers' bills.

Ofgem will now consult before making a funding decision. If approved in full or in part, the additional capital expenditure will flow into the Transmission Network Use of System (TNUoS) charge base, which is socialised across demand and generation users. For commercial buyers, TNUoS is already one of the larger non-commodity line items in a supply contract or pass-through bill. A significant uplift to the approved asset base would put upward pressure on future TNUoS tariffs, particularly for high-voltage industrial and commercial sites.

Key decision points and exposures to monitor:

• TNUoS demand tariffs for 2026-27 and beyond, set annually by National Grid ESO
• Ofgem's consultation timeline on the re-opener submissions, expected to run over several months
• The share of approved spend attributable to new low-carbon connections versus reinforcement of existing assets
• Pass-through contract structures, where TNUoS uplift lands directly on the buyer's bill
• Fixed-price contracts that bundle network charges, where suppliers may price in regulatory risk at renewal
• Multi-site portfolios with high half-hourly metered demand, which carry greater TNUoS exposure

For context, TNUoS demand charges already vary sharply by geographic zone and consumption profile. Any Ofgem-approved increase in the regulated asset base adds to the revenue that National Grid ESO must recover, and that recovery falls on demand users in proportion to their Triad exposure and zone.

Watch for Ofgem's initial response to the 25 proposals and whether the regulator signals a phased approval or a consolidated determination. Buyers approaching contract renewals in the next twelve months should ask their supplier or broker to model the TNUoS sensitivity under a range of approved-spend scenarios before locking in a term.