GLEC Framework v3.2 vs UK DEFRA emission factors — which one to use when

The most common question I get from UK shippers is whether they should switch from the DEFRA conversion factors they have used for a decade to the GLEC Framework v3.2. The honest answer is: it depends on who is going to read the disclosure. If only HMRC and DESNZ ever see it, DEFRA is fine and arguably more defensible. If a CDP questionnaire, a CSRD assurance file, or an EU shipper is in the chain, GLEC is the right base. The two tables agree on most numbers within about 5–10%. They diverge sharply on three things, and that is what this post is about.

Both frameworks publish per-tonne-kilometre emission factors. Both report well-to-wake (WTW), tank-to-wake (TTW), and well-to-tank (WTT) splits. Both are updated annually-ish — DEFRA (now under DESNZ) publishes mid-year; GLEC ships major versions every two to three years. As of March 2026 the live editions are GLEC v3.2 and DEFRA / DESNZ 2024 conversion factors (the 2025 set is in technical consultation; final publication is expected June 2026, and the 2024 factors stay live for the current reporting cycle).

Where they part ways is the methodology they sit underneath. DEFRA is built for UK organisational reporting under SECR and the Companies Act greenhouse gas regulations. GLEC is built for ISO 14083:2023 alignment, which is what CSRD assurance providers, CDP, and SBTi expect to see for Scope 3 Category 4 freight emissions. That difference in purpose drives most of the practical differences between them.

The headline number on a real UK lane

Take a worked example I run for clients trying to decide which way to point their calculator. Twenty tonnes of palletised dry goods, on a heavy articulated truck (HGV, gross vehicle weight above 33 tonnes, rigid 6+ axles in DEFRA terminology), running London to Edinburgh via the M1 / A1 / M74. Routed distance: 660 km. Trip purpose: regular contracted distribution, average load utilisation.

DEFRA 2024 publishes a WTW factor for “HGV (all diesel), articulated >33 t, average laden” of approximately 0.0672 kg CO₂e per tonne-km, which converts to 67.2 g CO₂e/tkm. The factor is built from UK government road-transport energy statistics and weighted by the UK fleet age and fuel mix, including the share of the fleet running on B7 diesel with the standard 7% biodiesel blend. The TTW share is 56.1 g/tkm and the WTT share is 11.1 g/tkm.

GLEC v3.2 publishes the equivalent factor for a European articulated truck >32 t gross combined weight, average laden, of approximately 62 g CO₂e/tkm WTW (after the v3.2 lane-utilisation adjustment up from the v3.0 figure of 60 g, which I wrote about in the v3.2 changes post). The TTW share is around 51 g/tkm; WTT around 11 g/tkm. The factor is built from European Commission and Eurostat road-freight statistics weighted across the EU-27 plus UK fleet operating in cross-border traffic.

So for the same shipment:

• DEFRA 2024: 660 km × 20 t × 67.2 g/tkm = 886,640 g, or about 887 kg CO₂e
• GLEC v3.2: 660 km × 20 t × 62 g/tkm = 818,400 g, or about 818 kg CO₂e

The DEFRA number is about 8% higher. That is not a methodological dispute, that is the UK fleet being older on average and running a slightly higher biodiesel blend than the cross-border EU average. Both numbers are defensible. Neither is wrong. If your London–Edinburgh shipment is on a fleet you can identify by carrier and vehicle class — the kind of carrier-specific Tier 2 adjustment I wrote up in the worked examples post — you should override both defaults with the actual fleet factor. But for a Tier 1 default-factor disclosure, the DEFRA number is the more conservative one for a UK lane, and that 8% gap is roughly what I see across most UK-domestic road freight.

When DEFRA is the right choice

Three situations where I tell a UK operator to stay on DEFRA.

SECR and Companies Act greenhouse gas reporting only. If the only emissions disclosure your business is regulated into is the UK SECR (Streamlined Energy and Carbon Reporting), the relevant framework is DEFRA / DESNZ. The UK Environmental Reporting Guidelines name the DEFRA conversion factors as the default basis. An auditor reviewing a UK-only SECR disclosure will not push back on DEFRA. They might push back on GLEC if you have not also explained why you used something other than the government-published number.

UK government procurement. The Crown Commercial Service procurement frameworks that touch carbon — PPN 06/21 for departmental procurement above £5 million, the carbon reduction plan templates — all reference DEFRA. If you are bidding into central government, DEFRA is the disclosure base. Submitting GLEC numbers without a DEFRA reconciliation makes the assessor’s job harder, which is not where you want to put friction in a tender.

UK-only road freight with no overseas leg. If your shipments load in Sheffield, deliver in Bristol, and never touch a port or a Channel crossing, DEFRA gives you a slightly more accurate number than GLEC for that lane — because the UK fleet weighting is closer to your actual operating environment than the cross-border EU weighting GLEC uses. The methodological aside is that DEFRA explicitly publishes factors for the UK fleet; GLEC explicitly publishes a Europe-wide average. UK-only operators should use the more representative table.

When GLEC is the right choice

And four situations where DEFRA is not enough.

Any lane that crosses a border. A shipment that loads in Manchester and unloads in Munich is by definition not a UK-domestic lane. The carrier’s tractor unit and trailer may swap on the Channel Tunnel shuttle, the trailer may continue with a Dutch or German truck after Calais, and the fleet weighting for either DEFRA or a single national table does not represent the actual journey. ISO 14083:2023 expects this kind of multi-jurisdictional lane to use a methodology-aligned framework with consistent treatment across borders. GLEC is that framework. DEFRA is not designed to cover the Munich leg.

CDP Climate questionnaire. CDP’s freight emissions question (currently C6.5 for Scope 3 Category 4 freight) accepts both ISO 14083-aligned and government-published factors, but the data quality scoring in C6.5a and the methodology disclosure in C6.7 favour GLEC alignment. I have walked through several CDP submissions where the difference between a B and an A- scoring band came down to declaring GLEC v3.2 with ISO 14083 data quality tiers versus declaring DEFRA without the tiering. The point is not that DEFRA is wrong; the point is that the CDP marking scheme is keyed to the ISO 14083 vocabulary. I covered this in detail in the Scope 3 Category 4 CDP guide.

CSRD assurance. CSRD ESRS E1.51 requires disclosure of Scope 3 emissions including upstream and downstream transportation. The assurance providers I have worked with through 2025 and into 2026 want to see ISO 14083 alignment and a documented data quality tier per mode. GLEC is the methodologically clean way to deliver that. You can deliver the same disclosure under DEFRA, but the assurance file gets thicker because you have to argue methodology equivalence at every step. With GLEC, the framework name on the cover page does the argument for you.

Anyone reporting to a shipper that reports to a shipper. If you are a UK 3PL whose customer is a manufacturer whose customer is a CSRD-reporting brand, your numbers flow up the chain. The brand at the top wants ISO 14083 alignment. The manufacturer in the middle will ask you the same. If you deliver DEFRA, the manufacturer has to convert or restate. If you deliver GLEC, the data passes through unchanged. The path-of-least-friction argument almost always wins in B2B reporting.

Where the two frameworks actually diverge

The 8% headline gap on UK heavy truck is fleet weighting, not methodology. Three other places the two frameworks diverge in ways that matter.

LNG marine fuel

DEFRA 2024 publishes LNG as a single bunker fuel category with a methane-slip assumption that is closer to the older steam-turbine engine class. GLEC v3.2 splits LNG by engine type — high-pressure dual-fuel versus low-pressure dual-fuel versus steam turbine — reflecting the ICCT methane slip measurements from 2020 and 2023. For a modern LNG carrier on a high-pressure dual-fuel engine, the GLEC WTW factor is roughly 8–12% lower than the DEFRA number. For an older low-pressure design, GLEC is roughly equal to or slightly higher than DEFRA. If you are running LNG in your bunker mix, the two frameworks will give you measurably different numbers on the same voyage. GLEC is the more methodologically current of the two.

Biofuel allocation

DEFRA gives a single per-litre factor for B7 diesel (the standard 7% biodiesel blend in UK road diesel as of 2024) and treats the biogenic carbon as having zero emissions on combustion. That is conventionally defensible but it leans on the lifecycle assessment of the biodiesel feedstock supply chain, which DEFRA pulls from the UK Renewable Transport Fuel Obligation (RTFO) data. GLEC v3.2 follows ISO 14083 and EU Renewable Energy Directive III (RED III) sustainability criteria: biofuels count as emission-reducing only where the feedstock and supply chain meet RED III thresholds. For UK road freight using RTFO-compliant biodiesel that does not meet RED III — which is a real chunk of the UK supply — GLEC will count the biogenic carbon and DEFRA will not. The difference per shipment is small (sub-1% for a B7 blend), but for a fleet running on B30 or higher biodiesel blends it adds up. The v4 GLEC draft is expected to tighten the RED III alignment further.

Refrigerated cargo (reefer)

DEFRA publishes a single “refrigerated transport” uplift factor that is added to the base road-freight factor for reefer trailers. The uplift is around 20% on the WTW number, reflecting the auxiliary load of the reefer unit. GLEC v3.2 disaggregates the reefer load by temperature band and by ambient operating temperature, with separate factors for frozen (below −18°C) versus chilled (0°C to 4°C) versus controlled-ambient cargo. For a chilled lane in cool ambient (most UK conditions, most of the year), GLEC gives a lower reefer uplift than DEFRA. For a frozen lane in warm ambient, GLEC gives a higher uplift. The DEFRA single-uplift number averages these. If you are running reefer at scale and your network bias is heavy on one temperature band, GLEC will track your reality more closely.

What about the new DESNZ 2025 factors?

The 2025 conversion factors are in technical consultation as of March 2026 and the final tables are expected June 2026. Two changes are likely to land. First, the LNG factor is expected to move to an engine-type breakout similar to what GLEC v3.2 already does — the DESNZ working group has referenced the ICCT methane slip data explicitly. Second, the heavy articulated truck factor is expected to move down slightly, reflecting 2023–2024 UK fleet renewal data and improved per-vehicle efficiency. The published number I expect is around 65 g CO₂e/tkm WTW for the >33 t articulated category, against the 67.2 g/tkm of the 2024 edition.

So the DEFRA / DESNZ table is converging on the GLEC numbers. That is the direction of travel and it has been since 2020. But the convergence is asymmetric: GLEC moves slightly faster on methodology, DEFRA stays current on the UK fleet specifics. They are not going to merge.

My honest opinion

If you only ship in the UK and report only to UK regulators, DEFRA is simpler and accepted everywhere. If any of your lanes cross a border or any of your shippers report to CDP or CSRD, GLEC is the right base. If you run both — UK domestic operations and EU export — pick GLEC and produce a DEFRA reconciliation for the UK-only legs as a footnote in your SECR disclosure. That is the cleanest position to defend in either direction.

The thing I would not do is run a hybrid factor table where some lanes use DEFRA factors and others use GLEC factors. Auditors hate it, the year-on-year deltas become noisy, and the explanation in the methodology section gets tortuous. Pick one base, document the choice, and override individual lanes with carrier-specific Tier 2 or Tier 3 data where you have it. The Tier 2/3 overrides are where the real accuracy gains live anyway — bigger than the GLEC-versus-DEFRA gap by a wide margin.

What this means for an existing calculator or report

If your in-house calculator is on DEFRA 2024 today and you have no CSRD or CDP exposure, do nothing. The 2025 factors will land in June and you swap then.

If you have any CDP or CSRD-aligned reporting in the chain, migrate to GLEC v3.2 for the next reporting cycle. Restate the prior year on the same basis if you can — year-on-year comparability matters and the restatement is methodologically defensible. Disclose the change explicitly.

If you are picking between the two for a brand-new build, default to GLEC v3.2 and add DEFRA as a named alternative factor table you can switch on for UK-only disclosure. That is what the EcoFreight calculator does — GLEC v3.2 is the default, with DEFRA available as a documented secondary factor table for clients who need it, and both versions stamped on every per-leg disclosure. The factor source is on the methodology page.

One acknowledged gap: I have not done a clean test of how GLEC v3.2 versus DEFRA 2024 plays for UK inland waterway freight. There is enough barge traffic on the Manchester Ship Canal, the Thames, and the Aire and Calder system to matter to some clients, and the two frameworks treat it differently — DEFRA has a UK-specific inland waterway factor, GLEC defers to a more generalised European inland waterway category. If you ship by barge in the UK and care about getting that lane right, email and we can compare notes; I would rather not guess the delta here.

Closing

DEFRA and GLEC are not competitors. They are two emission-factor tables with overlapping scope and different home regulators. The right answer for any given operator is rarely “all of one, none of the other” — it is “default to the one that matches your reporting audience, footnote the other where it adds value, and override both with primary data where you have it.” The 8% headline gap on UK heavy truck is real but it is well inside the per-shipment uncertainty band of either framework. The differences that actually matter are LNG, biofuel allocation, and reefer breakdown — and those are the lines on the factor table I would actually look at before deciding which way to point.

Sources

GLEC Framework v3.2, Smart Freight Centre, 2023 — smartfreightcentre.org. UK Government Greenhouse Gas Conversion Factors for Company Reporting (2024 edition), Department for Energy Security and Net Zero / DEFRA — gov.uk/government/collections/government-conversion-factors-for-company-reporting. UK Environmental Reporting Guidelines, March 2019 update (still current basis for SECR) — gov.uk. ISO 14083:2023 Quantification and reporting of greenhouse gas emissions arising from transport chain operations. ICCT methane slip studies (2020, 2023) for the LNG WTW divergence. UK Renewable Transport Fuel Obligation (RTFO) data for the biofuel feedstock supply chain underlying the DEFRA biodiesel factor.

The EcoFreight calculator runs GLEC v3.2 as the default and supports DEFRA 2024 as a named secondary factor table for UK-only disclosure. For the methodology details on data quality tiers, see the methodology page, and for how the version tag rides on every API response, the freight emissions API docs spell it out. Methodology critique gets a response faster than feature requests — email the team if a number here looks wrong.