Fuel Mix Disclosure: What Your Supplier Must Publish

Every licensed electricity supplier in Great Britain has to publish an annual fuel mix disclosure: a table showing the fuels behind the electricity it sold, as percentages, alongside a figure for the carbon dioxide produced per kilowatt hour. The obligation comes from the Electricity (Fuel Mix Disclosure) Regulations 2005 and the supply licence, and Ofgem reports on supplier performance against it¹.

The disclosure exists for one purpose: to let a household see what it is actually buying, and to compare one supplier's content with another's. Ofgem's guidelines state the aim is "to help suppliers with the presentation of the fuel mix information to help customers understand the information" and "to aid consumers when comparing the content of the fuel supplied by different suppliers"¹.

What it is not is a live reading of the grid. It is an annual, backward-looking statement about a supplier's own supply, and it sits apart from the wider environmental performance of the company behind it. Ofgem's supplier performance reporting is explicit that it "does not reflect wider environmental performance, or its energy mix"². Reading a disclosure well means knowing exactly what it covers, what it leaves out, and where the residual mix enters the picture.

What fuel mix disclosure is and why suppliers must publish it

Fuel mix disclosure is the mechanism that turns an invisible product into a labelled one. Electricity arriving at a meter is indistinguishable by source, so the disclosure substitutes a paper trail: the supplier states the proportion of its supply that came from each fuel category over the reporting year, and the emissions that supply carried.

The legal basis is the Electricity (Fuel Mix Disclosure) Regulations 2005, working through the standard conditions of the electricity supply licence. Ofgem's own performance reporting confirms the link, noting that it reports "on the performance of suppliers against their obligations under 'The Electricity (Fuel Mix Disclosure) Re[gulations]'"². The guidelines that govern presentation were published on 16 December 2005 and remain the reference document for how the information should be laid out¹.

The reason the obligation is placed on suppliers rather than on generators is that the supplier is the entity with the customer relationship. A household cannot audit a generation portfolio; it can read a table on a bill. The disclosure is therefore a consumer information measure first and an environmental accounting measure second.

It is worth separating this from the other reporting duties a supplier carries. Ofgem's supplier performance work covers a wide field, from smart metering installation targets to the Energy Company Obligation, and the fuel mix disclosure sits within that family of obligations rather than standing alone². The distinction matters when a household is trying to work out which published numbers describe the electricity itself and which describe the company's conduct.

What your supplier must show: fuels as a percentage, plus CO2 per kWh

The disclosure has two components, and both are mandatory. The first is the fuel mix itself: the share of the supplier's electricity that came from each source category, expressed as percentages that add to 100. The second is the environmental impact, expressed as carbon dioxide per kilowatt hour of electricity supplied.

Parliamentary material on the licence condition sets out the requirement plainly: the condition "requires suppliers to include data relating to a tariff's fuel mix and its environmental impact on at least one bill for" each financial year, and on all promotional materials³. That dual placement is deliberate. A bill reaches the existing customer; promotional material reaches the household still deciding.

The CO2 figure is a per-kWh intensity, not a total. It describes how carbon-intensive the supplier's own supply was, so two suppliers selling electricity into the same grid can publish different figures, because they bought different generation. It is also distinct from the national emissions factors used in official statistics, which describe the grid as a whole rather than one supplier's purchases.

For context on scale, the benchmark annual electricity consumption used in Ofgem's price cap work from 1 January 2026 is 2,700 kWh for a single rate household and 3,900 kWh for a multi rate household⁵. Those figures describe typical consumption, not supply content, but they show the volume a per-kWh intensity figure is applied to.

Nuclear waste: the extra statement for electricity from nuclear generation

Where a supplier's mix includes electricity from nuclear generation, the disclosure carries an additional statement about the radioactive waste that generation produces. This is a separate disclosure item rather than part of the percentage table, and it exists because nuclear generation has an environmental consequence that a carbon figure alone does not capture.

The logic is straightforward. A CO2 per kWh figure treats nuclear generation as low carbon, which it is in operational terms, but says nothing about spent fuel and the long-term management of radioactive waste. The extra statement is the mechanism that keeps that consequence visible to the household reading the table.

This is the point at which the disclosure's limits become clear. It is a disclosure of fuels and carbon, extended by one specific statement for one specific fuel. It is not a full life-cycle assessment, and it does not attempt to weigh construction, decommissioning or fuel processing for any generation type. A household reading a low carbon intensity figure should read it as a statement about generation emissions, not as a complete environmental account.

The same caution applies to the fuel categories themselves. A category such as "renewables" aggregates sources with quite different characteristics, and the disclosure does not break them apart. What the household gets is the supplier's own categorisation, presented to a common format so that comparisons between suppliers are at least possible.

Who enforces the requirement: the Gas and Electricity Markets Authority and supply licence conditions

Enforcement runs through the licence, and the licence is administered by the Gas and Electricity Markets Authority. The Authority is the statutory body established by section 1 of the Utilities Act 2000, and it is named as the administrator in energy legislation⁴. Ofgem is the Authority's operational face.

The mechanism is the standard licence condition. Ofgem's decision on consumer standards set out "our decision to implement modifications to the standard conditions of the gas and electricity supply licence"⁶, and the same instrument is how the fuel mix obligation is imposed and varied. A supplier that fails to publish, or publishes misleadingly, is in breach of a licence condition rather than of a standalone criminal provision.

It is important to be precise about what Ofgem's guidance documents do and do not do. The licence guides that Ofgem publishes for information for consumers, for switching, for smart metering and for safety and vulnerable consumer protections all state that the guide "does not modify or replace the conditions in the gas and electricity supply licences"⁷. The guides explain; the licence conditions bind. A household reading a guide should treat it as a route map to the obligation, not as the obligation itself.

The Authority also approves licences directly. When Tesla Energy Ventures Limited was granted an electricity supply licence covering Great Britain, the approval came from the Authority as the governing body: "the licence has been formally approved by its governing body, the Gas and Electricity Markets Authority"¹¹. New entrants take on the same licence conditions, including the disclosure duty, from the point they start supplying.

Ofgem's reporting on supplier performance is where the obligation becomes visible in aggregate. The regulator publishes performance data against supplier obligations, and the fuel mix disclosure regulations are among the obligations reported on². That gives a household a second route to scrutiny beyond the supplier's own table.

Where to find your supplier's fuel mix disclosure

There are three places to look, in order of reliability.

The first is the bill. The licence condition requires the data on at least one bill per financial year, so a household that keeps its bills will have the disclosure in its own records³. The second is promotional material, which the same condition covers: quotes, tariff pages and marketing must carry the data³. The third is the supplier's website, where many suppliers maintain a standing page for the current reporting year.

If the disclosure cannot be found, the supplier's own customer service route is the starting point. Ofgem's consumer guidance directs households to "review your current payments and debt repayments" as part of managing an account, and the same account channel is where a missing disclosure should be raised¹². For households in Northern Ireland, the position differs: electricity and gas suppliers and NIE Networks provide alternative forms of communication free of charge to consumers who need them, so a disclosure request can be made in an accessible format¹³.

Where a household is trying to establish who operates the network rather than who supplies the electricity, the Energy Ombudsman points to the Energy Networks Association website as the route to identifying the network provider¹⁴. That is a separate question from fuel mix, but it comes up when a household is assembling a picture of where its electricity comes from.

How to read and compare disclosures between suppliers

Comparison is the purpose the guidelines were written for, and it works best when a household reads three things together: the fuel percentages, the CO2 per kWh figure, and the reporting period.

Start with the percentages. They should sum to 100 and should be presented in a consistent format across suppliers, which is what the guidelines are designed to achieve¹. A supplier with a high renewable share will show it here. A supplier with a conventional generation portfolio will show that instead. Neither presentation is a judgement; the table is a description.

Then read the CO2 figure against the percentages. A mix can be low carbon without being entirely renewable, and a mix can be heavily renewable in percentage terms while carrying a carbon figure driven by the remainder. The two numbers answer different questions and should not be collapsed into one.

Then check the period. Because the disclosure is annual, a comparison between two suppliers is only fair if both are reporting the same year. A supplier that has changed its purchasing since the last disclosure will not yet show it.

Finally, keep the disclosure in its lane. Ofgem's supplier performance reporting states that it does not reflect "wider environmental performance, or its energy mix"². The disclosure is the energy mix document; it is not a sustainability report, and it does not cover a supplier's broader conduct. A household comparing suppliers on environmental grounds will need the disclosure plus other sources, and should treat the disclosure as the one part of the picture that is standardised and mandatory.

What fuel mix means for household energy independence

A fuel mix disclosure does not change what a household consumes, and it does not reduce dependence on the grid. What it does is make one part of that dependence legible. A household on a standard supply is buying electricity from a national system, through a supplier, at a price set by the market and the cap. The disclosure tells it what generation sat behind its own supplier's purchases in the last reporting year.

The dependence that remains is layered. There is dependence on the grid for delivery, on the supplier for the contract and the billing relationship, and on the generation mix for the carbon content of what arrives. The disclosure addresses only the third of those, and only retrospectively.

Where it has practical value for independence is in verification. A household considering a green tariff can read the supplier's own published percentages rather than relying on marketing language, and can compare that supplier with another on the same standardised basis¹. That is a real check, even though it covers the supplier's supply as a whole rather than one tariff in isolation.

The limits are worth stating as firmly as the benefits. The disclosure is annual, backward-looking, electricity-only, and silent on wider environmental performance³. It does not tell a household where its electricity physically came from, because electrons on a shared network cannot be traced that way. It does not cover gas at all. And it does not reduce the household's exposure to wholesale prices, to the price cap, or to the supplier's own financial position.

For households in Scotland, Wales and Northern Ireland, the generation context differs and the disclosure sits within a different set of published statistics. Welsh generation data, for example, records that around half of energy from waste came from renewable sources "with the other half coming from fossil fuel sources"¹⁵. Scottish housing statistics use an electricity emissions factor of 0.519 kg CO2 per kWh and a gas factor of 0.216 kg CO2 per kWh in the underlying SAP methodology¹⁶. Those are national accounting figures, not supplier disclosures, and they are useful precisely because they give a household a baseline against which a supplier's own CO2 figure can be read.

The Feed-in Tariffs scheme offers a related but separate route to understanding what is generated: Ofgem's quarterly statistics cover "installations that have completed the FIT accreditation process and are on the Central FIT Register" as of the reporting date¹⁷. That is generation data, not supply data, and it does not substitute for a fuel mix disclosure.

Read together, these sources let a household place its supplier's disclosure in context: the supplier's own percentages and carbon intensity, the national emissions factors, and the installed generation base. None of them removes the dependence. All of them make it measurable.