DEFRA emission factors 2026: why your electricity emissions fell 26% and how to report it

The 2026 DEFRA emission factors, now published by DESNZ, cut the UK electricity factor by about 26%, from 0.17700 to 0.13096 kg CO2e per kWh. Part of that is a cleaner grid and part is a method change. If your Scope 2 fell this year, explain why, and decide whether to restate prior years before anyone reads it as progress.

Every June the UK government publishes a new set of greenhouse gas conversion factors. Most sustainability teams update a spreadsheet, roll the numbers forward and move on. This year that habit could land you in an awkward conversation with your board, your auditor or a customer's procurement team.

What changed in the 2026 DEFRA emission factors

The Department for Energy Security and Net Zero published the Greenhouse gas reporting: conversion factors 2026 on 11 June 2026. DEFRA has not owned them for a while, but the name stuck, so that is what most people still search for.

The headline is electricity. The methodology paper describes "a significant change to the way the electricity emission factor is calculated". Until now, the factor combined generation data with the National Atmospheric Emissions Inventory, which meant a two-year lag between the year the emissions happened and the year the factor was published. The 2026 factor uses more recent Energy Trends data instead. The 2025 set was based on 2023 data; the 2026 set is based on 2025 data. The 2024 data year is skipped entirely.

So the drop you see is two years of grid decarbonisation landing at once, delivered by a change in method.

• UK electricity generated (Scope 2): 0.17700 kg CO2e per kWh in the 2025 set, 0.13096 in the 2026 set, a 26% fall.
• UK electricity transmission and distribution losses (Scope 3): 0.01853 kg CO2e per kWh in 2025, 0.01299 in 2026, a 30% fall.
• Data year behind the factor: 2023 for the 2025 set, 2025 for the 2026 set. The 2024 data year is skipped.

The knock-on effects reach anything that runs on grid power. The methodology paper names electric vehicles, rail and homeworking. Some transport factors moved for other reasons too, so check the "What's new" tab in the full set before assuming every change is about electricity.

Why this matters more than a normal annual update

Take a company using 1,000,000 kWh of grid electricity a year. With the 2025 factor that is 177 tonnes CO2e of location-based Scope 2. Run the same kWh through the 2026 factor and you get 131 tonnes. Forty-six tonnes gone, and nobody switched off a single light.

For an office-heavy business, electricity is often the biggest line in Scope 1 and 2. A 26% movement in that line can make a whole footprint look like it has turned a corner. If you set a reduction target against a 2019 or 2022 baseline, the gap to target just shrank on paper.

That is fine if you say so. It is a problem if a reader assumes it came from your reduction plan.

Do you need to recalculate your base year?

The GHG Protocol Corporate Standard lists "changes in calculation methodology or improvements in the accuracy of emission factors or activity data that result in a significant impact on the base year emissions data" as a trigger for recalculating base year emissions. It also says that changes in emission factors which "reflect real changes in emissions (i.e., changes in fuel type or technology) do not trigger a recalculation".

The 2026 electricity factor contains both. The UK grid really did get cleaner between 2023 and 2025. The time-lag fix is a methodology change. DESNZ itself says users "will need to decide whether they should adjust their previous years' estimates" and that, if they do not, they should be aware the 2024 data year has been skipped.

Our view, for what it is worth: most companies do not need to rebuild a five-year history over this. They do need to do three things.

1. Write down the decision in your base year recalculation policy, including your significance threshold, so next year's team does not reopen it.
2. Disclose the factor change in the methodology note of your SECR report, CDP response and annual report, with the size of the effect in tonnes.
3. Show your electricity consumption in kWh next to the emissions figure. kWh is the number you control, and it is the honest test of whether your reduction plan is working.

If your target is validated or close to validation, or electricity is a large share of your baseline, talk to whoever assures your numbers before you decide. The answer there may well be to restate.

Which factor year should you use?

The government describes the 2026 set as the factors for reporting emissions from UK activities in 2026. Calendar-year reporters with 2026 data should use the 2026 set. Companies with financial years that span two calendar years need a rule and need to apply it every year, whether that is the set matching the year the period ends or the set in force when most of the activity happened. Inconsistency between years causes more audit questions than either choice.

One more thing to check: the flat file version of the 2026 factors was republished on 31 July 2026 to fix values wrongly shown as zero for some hybrid, CNG and LPG car well-to-tank factors and some hotel stays. The full set was not affected. If your tool or spreadsheet imported the flat file in June, check it was refreshed.

What we are seeing on sales calls

The questions we hear from sustainability leads are rarely about the factors themselves. They are about the data the factors get multiplied by. Small offices on a landlord's service charge with no bill in the company's name. Gas meters nobody has read since the last audit. One buyer asked us for a checklist of the data they would need before anything else, which is the right instinct.

When a factor moves this much, the quality of your activity data matters even more, because it is the only part of the calculation that reflects what your business actually did. If 40% of your electricity is estimated from floor area, a factor change on top of that makes year-on-year comparisons close to meaningless. Fix the kWh first. For a refresher on what sits where, our guide to Scope 1 and 2 emissions walks through every source and both Scope 2 methods.

A quick checklist for your next report

• Confirm every electricity line uses the factor set your policy says it should, and note the version.
• Recalculate last year's figure with this year's factor as a side calculation, so you can split the change into "factor effect" and "consumption effect".
• Report location-based and market-based Scope 2. A renewable tariff hides this whole issue in the market-based number, which is another reason readers look at both.
• Update the methodology note in your SECR report and refresh any targets in your carbon reduction plan that were set against electricity emissions.
• If you have acquired businesses since your base year, deal with those structural changes at the same time. We wrote about how buy-and-build breaks carbon baselines for portfolio companies.

How Ella handles factor changes

Ella is AI-native carbon accounting software built as an agent. It applies the DESNZ factor set that matches each activity's period, records the factor version against every number, and keeps the source bill or meter read attached. When a new set is published, you can see the factor effect and the consumption effect separately, so the methodology note writes itself from data you can defend. Ella also chases the site contacts and data owners for the missing bills, which is where most of the real work sits, and produces your SECR summary and reduction roadmap with an audit trail, backed by expert support from Ella's team.