What to ask your suppliers now: CBAM emissions data

Every other part of UK CBAM — registration, returns, payment — waits politely until 2028. Supplier data does not. The emissions numbers behind your first return describe 2027 production, they live with your suppliers, and the realistic lead time for getting usable data out of an overseas mill is measured in months. This is the one workstream where starting now genuinely changes your outcome.

Why this can't wait for 2028

Three rules combine into a deadline nobody announces:

1. Actual data is measured over a calendar-year monitoring period. For 2027 imports, that means data for 2027 (or the year of production) — assembled from records the supplier keeps during the year.
2. Actual data must be independently verified — by a verifier accredited to the international standards the UK regime specifies (ISO/IEC 17029 and ISO 14065). Verification adds weeks to months after the data exists.
3. A return filed on default values cannot later be amended to actual data. Miss the window and the decision is permanent for that period.

So the sequence "file in May 2028, tidy the data up afterwards" does not exist. What you collect during 2027 is what your first return is made of.

What "good" supplier data looks like

For each covered good, from each producing installation (site, not company), you ultimately need:

• An emissions intensity: tonnes of CO₂e per tonne of product (per functional unit — the rules use tonnes of the good, with sector variants such as clinker for cement), covering direct emissions from the production process within the UK's defined system boundaries.
• Precursor detail: the covered input materials (crude steel in fasteners, clinker in cement, ammonia in nitric acid) and their emissions, since these are charged as part of the final good. If the producer buys precursors in, their data request cascades one step up the chain.
• The monitoring period: which calendar year the figures describe.
• Verification status: verified by whom, accredited by whom, against which standards — or a realistic statement that verification is planned.

If a supplier already produces emissions reports for EU CBAM, you are most of the way there: the UK methodology is deliberately designed for broad interoperability, and a transition route exists for verifiers accredited under the EU framework. "Send me what you prepared for your EU customers" is a perfectly good opening move — the gaps (UK system-boundary differences, verification standard details) are refinements, not a restart.

The fallback: default values

No data? You use the government default value for that good — one figure per product type, published before the regime starts (the numbers themselves are still pending). Defaults are legitimate and final: no evidence chase, no verification. The catch is the price. The government has signalled defaults will be set so there is no advantage over actual data — and you should expect efficient producers' real numbers to beat them, sometimes substantially.

The rules also constrain mixing: you can use actual data for a final good with defaults for its precursors, but not actual precursor data under a defaulted final good. Practically: prioritise real data for your highest-value, highest-volume lines, take defaults on the long tail, and make each call deliberately — because after filing, it is locked for that period.

How to run the collection — a realistic plan

1. Rank your exposure. From your import ledger: covered lines by customs value and weight, grouped by supplier. The top handful of suppliers usually cover most of the liability.
2. Ask now, in writing. One email per supplier (template below). The goal of round one is not perfect data — it is discovering who can respond, who already does EU CBAM, and who will need a year of chasing.
3. Accept their format. You will receive spreadsheets in every layout imaginable, PDFs of certificates, and screenshots. Fighting formats loses months; normalising them is a software problem (it is precisely the one CBAMReturn exists to solve).
4. Log the gaps as money. For every line without data, note that it will ride on defaults. When the default values publish, that gap list becomes a priced cost of inaction — the most persuasive document you can put in front of a slow supplier (or your own board).
5. Re-run quarterly. Suppliers' EU CBAM cycles keep generating fresher data; your mix changes; 2028 imports will need recent verified years.

An email you can send today

Subject: Carbon emissions data for goods we buy from you — UK CBAM

From 1 January 2027 the UK is introducing a Carbon Border Adjustment Mechanism (UK CBAM), a carbon charge on imports of iron & steel, aluminium, cement, fertiliser and hydrogen products. As an importer of your products into the UK, we will be required to report the emissions embodied in the goods we buy from you, and to pay a charge based on them.

We can use either your actual, independently verified emissions data — or UK government default values. Real data is likely to work in both our favour, so we would like to start with three questions:

1. Do you already prepare embedded-emissions data for EU CBAM customers? If so, please share your most recent emissions report for the products we purchase.
2. If not: can you provide, per production site, direct emissions per tonne for these products for the current year, including the main input materials (precursors)?
3. Is your emissions data independently verified, and by whom?

This will be a standing annual requirement, so we'd also like to know who in your team should own it going forward. Happy to arrange a short call.

Non-committal replies are normal at first. What matters is starting the clock, identifying the capable suppliers early — and creating the paper trail that shows you asked.

Red flags in what comes back

• Company-wide carbon footprints (corporate scope 1/2/3 totals) — not usable; CBAM needs per-installation, per-product intensity.
• Product carbon footprints on the wrong boundary — a cradle-to-grave PCF or an EPD is a clue the supplier measures things, but the CBAM figure needs the regime's specific system boundaries.
• Round numbers with no methodology or year attached — unverifiable, and unlikely to survive verification.
• "Our government doesn't require this" — irrelevant; the requirement follows the goods to the UK border.

Sources

• HMRC CBAM policy summary, April 2026 — data options, verification standards, mixing rules
• Draft CBAM (Emissions and Verification) Regulations and System Boundaries document, April 2026 — monitoring periods, intensity calculation, verifier accreditation
• Finance Act 2026, Schedule 17 — default values framework and the no-amendment rule