A sourced map of the Great Britain energy system in May 2026

Pillar 1: The system today, in one paragraph and a jump back to the section above

For a two-minute read, the section directly above this one is the whole map: who decides what, what was decided in the past year, and what is still in flight. NESO has been running for nineteen months. The Capacity Market T-4 for 2029 to 2030 cleared 40.1 gigawatts in February 2026. The LTDS publishes Stage 2 on 29 May 2026 under the third Ofgem derogation letter. REMA Phase 2 was decided in summer 2025 in favour of Reformed National Pricing. CSNP methodology was approved in April 2026, with T-CSNP due June 2026 and the first full CSNP by end-2028. The section above carries the current state; the pillars carry the depth.

Section anchor: Where the Great Britain energy system stands this month.

Pillar 2: How Great Britain built one electricity system across five eras, 1881 to 2026

The current institutions are intelligible only against the five eras that shaped them. The pioneer era (1881 to 1926) produced 505 separate electricity undertakings on different currents, voltages and frequencies until Parliament chose central coordination through the Central Electricity Board. The state-control era (1926 to 1979) built the National Grid, nationalised supply on Vesting Day in 1948, and ran the integrated system through the CEGB. Privatisation (1979 to 2003) broke up the CEGB under the 1989 Electricity Act, opened the Pool wholesale market in 1990, and created Ofgem in 1999. Decarbonisation (2003 to 2019) put the Climate Change Act 2008 in place, launched Contracts for Difference under the Energy Act 2013, and produced the first coal-free 24 hours in April 2017. The net-zero era (2019 to present) added the net-zero amendment in June 2019, the Energy Act 2023, the launch of NESO on 1 October 2024, and the Clean Power 2030 commitment in December 2024.

The 1989 Electricity Act is the parent of every institution except NESO. Where LTDS is mandated through SLC 25.2 of the Electricity Distribution Licence, the SLC is the 1989 Act's child. The 2008 Climate Change Act is the framework that forces every other decision toward decarbonisation, with carbon budgets set by Parliament every five years. The Energy Act 2023 is the framework for the current era, with NESO at the centre and whole-system planning rather than market regulation as its remit.

Open: History 1881 to 2026, with five era anchors and a metric timeline.

Pillar 3: The network and the LTDS, from 400 kilovolts down to a household connection

The third pillar is the engineering blueprint. The voltage cascade runs from the 400-kilovolt and 275-kilovolt transmission network operated by the three transmission owners (National Grid Electricity Transmission in England and Wales, SP Transmission in southern Scotland and SSEN Transmission in northern Scotland), down through 132-kilovolt distribution, 33-kilovolt and 11-kilovolt feeders, to the 230-volt service that arrives at a meter. Each step is owned by a licensed transmission or distribution operator under conditions issued by Ofgem under the Electricity Act 1989. The Distribution Network Operators (DNOs) plan and run the part of the grid below 132 kilovolts; the Transmission Owners (TOs) plan and run the part above.

The Long Term Development Statement is the standardised, machine-readable model of the distribution network that every DNO publishes under SLC 25.2.¹ The 30 April 2024 Ofgem Direction moved the LTDS from Excel files to a validated CIM data model, with phased delivery across Stages 1, 2 and 3. The third derogation letter of 13 May 2026 reshaped Stage 2 contents while holding the publication date.² Stage 2 publishes on 29 May 2026; Stage 3 publishes on 30 November 2026. The LTDS page on this workspace is the gold-standard reference for how the data model is structured, how mRIDs resolve, how SHACL validates a CIM profile, and where to download the actual published artefacts.

Open: Network, Voltage cascade, Connections queue, LTDS explained, System resilience.

Pillar 4: Markets, from a day-ahead price to a settlement run and a Capacity Market clearing

The fourth pillar is how the megawatts get bought and how the costs flow back to a consumer bill. The wholesale day-ahead market clears every half-hour under the Reformed National Pricing arrangement that was confirmed in the summer 2025 REMA Phase 2 decision.¹² The balancing mechanism, operated by NESO, accepts bids and offers to reconcile demand and supply minute by minute. The Capacity Market procures the obligation to be available at peak demand four years ahead, with a top-up T-1 auction one year ahead. The 2029 to 2030 T-4 cleared in February 2026 at twenty seven pounds ten per kilowatt year for 40.1 gigawatts; the 2026 to 2027 T-1 cleared in March 2026 at five pounds per kilowatt year for 7.2 gigawatts.⁶

Contracts for Difference are the primary support mechanism for new low-carbon generation. AR7 reported on 14 January 2026 with a record 8.4 gigawatts of offshore wind awarded.¹³ The interconnectors give Great Britain 9.8 gigawatts of cross-border capacity today to France, Belgium, the Netherlands, Norway, Ireland and Denmark, with Viking Link and Greenlink lifting that toward 18 gigawatts by 2030. The consumer cost chain runs from wholesale spend through network charges to retail margin to bill; the Ofgem Default Tariff Cap sets the ceiling for non-fixed tariffs each quarter.

Open: Markets (with interconnectors absorbed in line with the May 2026 consolidation decision), Electricity generation mix, Live generation dashboard.

Pillar 5: Energy data, from the smart meter to the settlement run to the CIM profile

The fifth pillar is the data layer. The energy data routes cover six sub-domains. Actors and roles names who produces, governs and consumes each dataset. Physical data generation covers smart meters, telemetry from the network, and the 33 million Meter Point Administration Numbers under migration to half-hourly settlement.⁸ The taxonomy collects 87 named data types in 13 categories with their licence, custodian and consumer. Lifecycle and settlement walks a representative meter from measurement to bill, including the BSC P408 settlement run. Rules, governance and privacy covers UK GDPR after the Data (Use and Access) Act 2025, the energy-smart Data and Privacy Framework, and the regulatory landscape.⁷ Planning and future covers Future Energy Scenarios, the SSEP, and the CSNP.^{9 10} CIM and interoperability covers the Common Information Model profiles (CGMES 3, IEC 61968-13, IEC 61970-301) and the BSI CIM Engagement Hub.^{3 4 5} Global comparison places GB next to the EU, the United States, Australia and the Nordics.

Two reforms make this pillar the centre of gravity for the next two years. The MHHS programme cuts over in July 2027, after which all electricity settlement is half-hourly for every consumer, not just half-hourly for those on a Time of Use tariff. The LTDS move to CIM (covered in Pillar 3) is the first GB instance of a validated machine-readable distribution model published on a regulator-set cadence; the same data-model approach is expected to spread to transmission and gas over the rest of the decade.

Open: Actors and roles, Physical data generation, Taxonomy, Lifecycle and settlement, Rules and governance, Planning and future, CIM and interoperability.

Pillar 6: Energy vectors, the molecule-system routes beside electricity

The sixth pillar covers the energy vectors that sit alongside electricity. Gas remains the largest by volume; the National Transmission System runs the 7,600-kilometre high-pressure backbone with daily flow data published by National Gas. Hydrogen is the smallest by volume today but the most contested in policy terms; the routes split between green (electrolysis from renewable electricity), blue (steam methane reforming with CCUS) and pink (electrolysis from nuclear), with the Wobbe Index governing what can be blended into the existing gas network. Heat is the system's single largest source of household carbon emissions; the move to heat pumps and heat networks (under Ofgem regulation from 27 January 2026¹⁴) is the demand-side answer. Nuclear is the firm low-carbon dispatchable source; the Wylfa site contract for three Rolls-Royce small modular reactors was signed in April 2026, with final investment decision expected in 2029 and in-service mid-2030s.¹⁸ CCUS is the industrial-decarbonisation play; the Track 1 and Track 2 clusters in Teesside, Humber, Merseyside and Aberdeen sit inside the long-term funding model. Oil sits at the smallest policy salience among the vectors but remains in the picture for transport, petrochemicals and as a coupling fuel for refining.

Open: Gas, Hydrogen, Heat, Nuclear, CCUS, Oil.

Pillar 7: Digital infrastructure, scenarios, tools and the dictionary

The seventh pillar covers the rest of the workspace. Digital infrastructure absorbs the data-sharing routes (DCC, DSI, the four-domain DSI architecture, the SEC and the REC). The Scenarios library holds ten documented stakeholder trade-off cases: connections queue reform, DSO flexibility procurement, supplier failure and redress, the LTDS to CIM sequencing, MHHS readiness and cost, the price cap versus resilience trade-off, reinforcement versus connection speed, smart-meter data sharing, the strategic-planning trade-off, and the heat-network complaint path. Tools and engineering tools provides calculators for household bills, per-unit base, transformer ratio, voltage drop, and a stack of engineering checks behind the embed. The Dictionary is the searchable glossary across the whole workspace; tooltip definitions on every page resolve into it.

Open: Digital infrastructure (with data-sharing absorbed in line with the May 2026 consolidation decision), Scenarios library, Tools and engineering, Dictionary.