Fuel Mix Disclosure

1) UK Fuel Mix Disclosure (FMD): regulatory context

In Great Britain, Fuel Mix Disclosure (FMD) is a legal requirement introduced by The Electricity (Fuel Mix Disclosure) Regulations 2005 (SI 2005/391). The regulations require electricity suppliers to disclose to customers (and potential customers) the mix of fuels used to generate the electricity they supply for a full disclosure period. The disclosure period runs from 1 April to 31 March, and suppliers must disclose the information by 1 October each year. The obligation is incorporated into electricity suppliers’ standard licence conditions and is now Standard Licence Condition 21 (SLC 21).

Official Ofgem guidance: Fuel Mix Disclosure (FMD) — Ofgem

2) What the data represents (and what it does not)

Fuel Mix Disclosure figures are an accounting / contractual disclosure. They describe how suppliers attribute the electricity they sell to fuel categories based on evidence and rules under the FMD framework. They do not describe the real-time physical flow of electricity (“which electrons you received”) on the network.

EnergyMix presents supplier-declared Fuel Mix Disclosure data and related metrics side-by-side (e.g., 2025 vs 2024), so users can compare suppliers and track changes over time. Missing values are shown as “–”.

3) Evidence and certificates (REGOs and Guarantees of Origin)

The UK uses Renewable Energy Guarantees of Origin (REGOs) as a core evidence mechanism for renewable electricity claims within the FMD framework. Ofgem also provides guidance on how Guarantees of Origin (GoOs) are treated for Great Britain Fuel Mix Disclosure.

Notably, Ofgem states that from the disclosure period beginning 1 April 2023 onwards, GoOs are no longer recognised for use in GB FMD.

Reference: Guarantees of Origin (GoOs) — Ofgem

4) Reporting periods shown on EnergyMix

The Fuel Mix Disclosure framework operates on an annual disclosure period (1 April to 31 March). EnergyMix may display multiple years side-by-side (for example, “2025” vs “2024”) to support year-on-year comparison. Where a supplier’s published disclosure is not available or a value is not provided, EnergyMix shows a dash (“–”) rather than estimating.

5) Metrics and formatting rules

Fuel percentages

Fuel category values (Gas, Coal, Nuclear, Renewables, Other) are shown as percentages. EnergyMix formats percentages for readability: whole numbers are shown without decimals (e.g., 8 not 8.0), otherwise one decimal place is shown.

Emissions (g/kWh)

Emissions are shown as whole-number g/kWh for readability. These values are presented as disclosed/attributed under the relevant published data source for that supplier/year.

Nuclear waste (mg/kWh)

Nuclear waste values are shown as mg/kWh for readability. Where a source provides nuclear waste in g/kWh, EnergyMix converts units using: mg/kWh = g/kWh × 1000. The display uses sensible significant figures to avoid implying false precision.

6) UK Average and Residual Fuel Mix

EnergyMix includes two benchmark rows for context:

UK Average: an official published average fuel mix on an electricity supplied basis.
Residual Fuel Mix: the residual mix used for the portion of supply not backed by specific attribute evidence, published in the annual fuel mix disclosure data table.

Reference dataset (government publication): Fuel mix disclosure data table — GOV.UK

7) Limitations and interpretation

Fuel Mix Disclosure is an accounting disclosure, not a physical trace of electrons delivered to end users.
Supplier statements can differ in presentation and detail; EnergyMix displays values as published and avoids estimating missing data.
Comparisons should be made in the context of the disclosure period and the rules for certificates/attributes in Great Britain.

8) Sources and updates

The supplier rows link to each supplier’s published disclosure or source page (where provided). Benchmark values (such as UK Average and Residual Fuel Mix) are based on official publications (Ofgem guidance and the government’s fuel mix disclosure data tables).

Fuel Mix Disclosure is typically updated annually after the relevant regulatory deadlines. EnergyMix updates its dashboard as new disclosures and official tables become available.

Contact and citation

If you have questions about the methodology, data sources, or interpretation of the Fuel Mix Disclosure presented on this site, please contact:
Email: energymixuk@gmail.com

Citation guidance

If you use data from this dashboard in articles, reports or academic work, please cite:

EnergyMix (2026). National Grid Live – UK Electricity Generation & Carbon Intensity. https://energymix.uk/ (accessed 31 January 2026).