Which? analysis reveals stark divide in sustainability performance among energy suppliers
The UK’s transition to cleaner energy continues to gather pace, with renewable generation rising 5.7 per cent year-on-year and accounting for more than half of National Grid electricity last year, according to UK government data.
Yet a new Which? sustainability ranking reveals a divide in how energy suppliers are approaching green initiatives.
The consumer champion assessed 15 energy suppliers to reveal which firms are leading the way on sustainability. Each provider was evaluated across three critical pillars: their renewable energy sourcing, their operational greenhouse gas emissions and the practical support they offer to help households cut carbon.
Four suppliers earned the coveted Which? Eco Provider endorsement for 2026, while two of Britain’s largest energy suppliers occupied the lower and middle tiers of the table with higher emissions and corporate links to fossil fuels limiting their scores.
At the bottom of the table were Scottish Power and E (Gas & Electricity), both scoring zero per cent.
Scottish Power received a score of zero per cent because it chose not to participate in Which?'s research questionnaire this year.
E (Gas & Electricity) received a score of zero per cent. It does not generate or purchase renewable power, sell green gas, offer a time-of-use tariff or provide low-carbon measures, and it has below-average solar export rates. The supplier also did not provide the greenhouse gas emissions data required for the assessment.
Outfox Energy scored slightly higher at five per cent. While it offers time-of-use tariffs, it does not generate or purchase renewable power or sell green gas, which limits its score. It also did not provide the greenhouse gas emissions data required for the assessment.
At the top of the rankings are the suppliers setting the benchmark for sustainability in the energy sector, earning themselves the coveted status as a Which? Eco Provider.
Good Energy and Octopus Energy topped the table as the joint highest-scoring suppliers overall, with impressive scores of 85 per cent each.
Both providers achieved top scores of five out of five for helping households cut carbon, with Octopus praised for its range of flexible tariffs and extensive green tech installations, while Good Energy stood out by matching customers’ electricity use with renewable power generated in the same half hour 90 per cent of the time.
Ecotricity scored 75 per cent, achieving the highest individual renewable energy score of 11 out of 12.
100Green scored 70 percent and was the only firm evaluated to offer 100 per cent green gas. It also stands out as the only provider with a unique tariff designed to protect wildlife and fragile ecosystems.
Notably, Good Energy and Ecotricity have retained their Eco Provider status every year since the survey began in 2021.
Some of the largest energy firms occupied the middle of the table, with British Gas and EDF Energy each scoring 55 per cent.
British Gas and EDF Energy recorded among the highest operational greenhouse gas emissions among suppliers in the research, each receiving a low score of one out of three. While both generate and buy renewable power, they also have links to fossil fuels.
British Gas’ parent company operates gas-fuelled peaking plants (which run when there is high power demand) while EDF Energy has contracts with gas power plants.
However, both performed well in helping consumers reduce their carbon footprints. EDF scored highly in this category, scoring four out of five point. An impressive one in five (20 per cent) of British Gas customers are on a time-of-use tariff or participate in its “saving sessions”.
While switching to a top-performing provider sends a clear signal to the market, households can also cut their bills and carbon footprint without changing energy supplier. Shifting energy use away from the weekday peak of 4-7pm can unlock rewards through schemes like British Gas' PeakSave Green Flex and Octopus Energy's Power-ups.
Even without specific supplier incentives, consumers can drive down costs themselves by trimming daily usage. Simple steps like utilising appliance eco programmes, running full laundry loads, drying clothes outside, and utilising hot water timers ensure households only use the energy they strictly require.
Emily Seymour, Which? Energy Editor, said:
“Our research shows there are big differences in how energy firms are approaching green initiatives. If this is something you care about, it’s worth checking how your supplier performs against its competitors.
"Some providers are taking far more action than others, so don't assume they're all the same. If your supplier isn’t performing as well as you'd like, switching to a top-performing company sends a clear message to the market.”
-ENDS-
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Total score out of 20 shown as a percentage. Data collected in March 2026. Where companies didn't provide usable data for a question, they scored zero. Co-Op Energy is operated by Octopus Energy and scores the same. Sainsbury's Energy is a trading name of E.on Next and scores the same. Scottish Power did not participate in our research so scores zero.
Research Methodology:
In March 2026 Which? asked 15 GB energy providers for information regarding their sustainable practices via a detailed questionnaire.
Companies were scored using a points-based system across three core categories, with a score of zero applied to any question where a provider failed to deliver usable data.
Renewable Energy (Maximum 12 Points):
Firms scored points for closer connections to renewable power sources including generating it themselves and also for buying it directly from renewable generators via Power Purchase Agreements or similar contract arrangements.
Which? checked which providers had recently built new renewable generation capacity and sold green gas.
For the first time, brands were asked what proportion of the electricity used by their domestic customer base was directly matched with renewable electricity being generated in the same half hour. This addresses standard annual reporting where a "100% renewable" claim can be backed by REGO certificates from solar power generated during a few sunny months to offset fossil-fuel power used in the winter.
Helping Customers Cut Carbon (Maximum 5 Points):
The assessment looked at whether brands offer customers routes to low-carbon installations, including solar panels, heat pumps, battery storage and EV chargers.
Providers were compared on products (such as Time of Use tariffs) offered that encourage households to cut energy use at peak times, which reduces the need for back-up fossil fuel generation by the National Grid.
Which? rewarded competitive Smart Export Guarantee rates for customers who sell any excess electricity generated back to the grid.
Greenhouse Gas Emissions (Maximum 3 Points):
The assessment evaluated the emissions involved in the firms' own operations.
Firms were also assessed on whether they could provide Scope 3 emissions, which include the emissions of all the gas and electricity used by their customers.
Rights of replies - deadline COP 11th June:
A British Gas spokesperson said: We’re pleased Which? has given us the top score for helping customers cut their carbon footprint. It reflects the practical support we offer to households, from time-of-use tariffs for customers with electric vehicles, heat pumps or battery storage, to smart ways of shifting demand away from peak times. Our saving sessions, through our PeakSave scheme are making a real difference, giving people the choice of taking part on Saturdays or Sundays, with more than a million customers having already saved over £36 million on their bills while cutting nearly 3,000 tonnes of carbon emissions.”
An EDF Energy spokesperson said: We're pleased that Which? recognised EDF's strong performance in helping customers cut carbon, awarding us 4 out of 5 in this category. EDF is one of the UK's largest producers of low-carbon electricity, with all of our generation coming from nuclear power and a growing renewables portfolio. Our mission is to help deliver an Electric Britain by investing in new low-carbon generation and helping customers electrify their homes, transport and businesses through competitive tariffs, EV charging, solar, batteries and heat pumps. We welcome the feedback from Which? and will continue investing in the technologies and infrastructure needed to support the UK's transition to a lower-carbon energy system.
Which? reached out to E (Gas & Electricity) but they did not provide a comment.
An Outfox Energy spokesperson said: Outfox has consistently offered the cheapest fixed tariffs in the UK market, averaging over £200 below the price cap. During a period of acute financial hardship for millions of households, we believe keeping energy genuinely affordable is itself a meaningful and undervalued form of sustainability. Green gas and REGO-backed tariffs carry real cost premiums that ultimately fall on consumers. In a cost-of-living crisis, ensuring people can afford to heat their homes must be part of any honest assessment of what responsible energy supply looks like. Since 1st April 2026, Outfox Energy is a participant in the SEG scheme and offers a SEG tariff.
Which? reached out to Scottish Power but they did not provide a comment.
About Which?
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