Scope 3 Is Coming for Your Business - Even If You Have Never Heard of It

The GHG Protocol - the global standard for measuring greenhouse gas emissions - divides a business's carbon footprint into three "scopes." The terminology sounds technical; the underlying concepts are not.

For most SMEs, Scope 1 and Scope 2 together represent the immediate ask. Scope 3 is broader - and the reason your largest customers are about to contact you.

Understanding the three scopes is the starting point. The next question is: why does any of this affect your business?

Large companies are not asking for supplier emissions data out of curiosity. They are asking because their own reporting obligations require it.

CSRD: the EU regulation that reaches into UK supply chains

The EU's Corporate Sustainability Reporting Directive (CSRD) requires large companies to disclose detailed environmental data - including Scope 3 emissions from their supply chains. Under the EU Omnibus I package adopted in February 2026, the obligation applies to large companies only (broadly 1,000+ employees and €450m+ turnover). The direct obligation does not land on most UK SMEs - but it does land on the large companies those SMEs supply.

If you supply a UK subsidiary of a large EU company, or export into EU supply chains, your customer's parent entity may already be preparing CSRD disclosures. Scope 3 Category 1 - purchased goods and services - requires data from suppliers. That data is you.

UK frameworks: SECR, CDP, SBTi, and voluntary net zero commitments

UK large companies under Streamlined Energy and Carbon Reporting (SECR) are not currently required to report Scope 3. However, many have made public net zero commitments - voluntary pledges outside SECR that require Scope 3 data to verify. The CDP Supply Chain programme and Science Based Targets initiative (SBTi) both require Scope 3 reporting and are widely adopted by FTSE 100 and FTSE 250 companies.

A practical example: a legal firm supplying a FTSE 100 bank. The bank has committed to SBTi and CDP disclosure. Its Scope 3 Category 1 includes the emissions embedded in legal services it buys. The bank's sustainability team sends a questionnaire to its top 200 suppliers asking for Scope 1 and 2 data. The legal firm has one month to respond. If it cannot, the procurement team notes a data gap. Gaps accumulate into a supplier risk score.

A large company (Tier 0) needs Scope 3 data from its direct suppliers to complete its CDP or SBTi disclosure. It sends data requests to Tier 1 suppliers. Those Tier 1 suppliers - often medium-sized businesses with their own sustainability commitments - then send requests to their Tier 2 suppliers. The cascade moves down the chain.

At each tier, the request looks slightly different - different forms, different platforms, different deadlines - but the underlying ask is the same: Scope 1, Scope 2, and possibly a summary of Scope 3. The three frameworks driving most UK requests are:

• CDP Supply Chain programme: corporate members request emissions data from their suppliers via CDP's standardised questionnaire
• EcoVadis: a supplier sustainability rating platform used by procurement teams at large manufacturers, retailers, and professional services firms; includes a carbon disclosure module
• SBTi Science Based Targets for SMEs: the Science Based Targets initiative has a dedicated SME pathway - increasingly, large-company SBTi commitments include a supplier engagement target requiring a percentage of suppliers to set their own science-based targets

The form itself is rarely intimidating. The problem is that answering it accurately requires data most SMEs have not previously organised: consolidated energy consumption figures, a documented calculation method, and a written sustainability policy. None of that is difficult to produce - but all of it takes time if you start from zero on the day the request arrives.

The phrase "Scope 3 reporting" suggests a complex undertaking. For SME suppliers at the first tier, the initial data request is considerably more contained than that phrase implies.

Note what is not on this list for a first-tier SME supplier: full Scope 3 calculation, life cycle assessment, detailed waste data, or supplier screening records. These may appear in later requests or as the customer relationship matures. At the initial request stage, Scope 1 and Scope 2 are the minimum viable answer.

Supplier questionnaires often distinguish between measured emissions (from direct meter readings or calibrated monitoring) and estimated emissions (calculated from activity data using published conversion factors). The distinction matters because buyers sometimes ask which methodology you used.

Measured emissions

Measured means reading actual consumption from meters or utility bills that show metered kWh figures. For most SMEs on standard supply contracts, the bills already provide metered data. If your bills show kWh, you are measuring - not estimating. You are applying a published conversion factor to turn a measured energy figure into an emissions figure.

Estimated emissions

Estimated means you are deriving activity data from secondary sources where direct measurement is not available - for example, calculating fuel combustion from mileage logs rather than from a fuel flow meter, or estimating electricity use from equipment specifications rather than from a meter reading. For Scope 3 categories such as employee commuting or supply chain emissions, estimation is standard practice even for large companies.

Most buyers accept estimated Scope 1 and Scope 2 from SME suppliers, particularly for first-time submissions. The GHG Protocol - the methodology standard underpinning CDP, SBTi, and CSRD - explicitly includes activity-based estimation as a valid and recognised methodology. Estimated is not inferior; it is the standard approach for the vast majority of SME suppliers.

What makes an estimate credible

• A published conversion factor is cited - DEFRA publishes annual UK-specific factors and they are freely available
• The activity data source is documented - specifically, kWh figures from utility bills for the relevant 12-month period
• The calculation is shown - total kWh multiplied by the conversion factor, producing a kgCO2e or tCO2e figure
• The baseline year is stated - so the buyer knows what period the figure covers

What makes an estimate not credible

• A round number with no methodology cited ("approximately 5 tonnes")
• No conversion factor referenced
• No source data identified ("based on rough estimates of our energy use")
• A figure that cannot be reproduced from the inputs provided

Building your baseline is a three-step process requiring no specialist knowledge or paid tools. Total time for a single-site business is typically under two hours.

1. 1
   Collect 12 months of gas and electricity bills. Use your most recent complete calendar year or financial year as the baseline period. If you are on a smart meter, download the monthly consumption data from your supplier's portal. If you receive paper or PDF bills, note the kWh figure from each bill and total them. You need one number: total kWh of gas consumed, and total kWh of electricity consumed, for the same 12-month period.
2. 2
   Apply the DEFRA conversion factors. For electricity: multiply total kWh by 0.207 to get kgCO2e (this is the UK grid location-based factor; check the current DEFRA spreadsheet for the most recent published figure). For gas: multiply total kWh by 0.183 to get kgCO2e. Divide by 1,000 to convert to tCO2e. These two figures are your Scope 1 (gas) and Scope 2 (electricity) emissions baseline.
3. 3
   Write a one-paragraph carbon baseline statement. Include: your baseline year, your Scope 1 figure, your Scope 2 figure, the methodology used (activity-based estimation using DEFRA conversion factors), and a note on the data sources (utility bills for the period). This paragraph becomes the foundation of your sustainability policy and the answer to the first two rows of any supplier questionnaire.

What to do with the number once you have it

Put the figure in your sustainability policy as your baseline year. Set a specific, time-bound reduction target - for example, a 10% reduction in combined Scope 1 and Scope 2 within two years. Log any actions you take: LED lighting, insulation, renewable tariff switch. Each action becomes evidence of progress against your baseline.

A documented baseline with a reduction target is a materially stronger answer to a supplier questionnaire than a blank field or vague aspiration. It shows the buyer that you track performance and that your commitment has a number behind it.

When the questionnaire arrives and you answer it in two hours - with documented figures, a cited methodology, and a written sustainability policy - you become the supplier who does not create friction. The businesses that cannot answer get chased, escalated, or deprioritised. The ones that answer accurately and quickly become low-risk suppliers. In procurement terms, that is a commercial advantage.