Your Customers Want Your Carbon Footprint: How to Answer With Confidence

It usually starts with an email. A big customer sends a supplier questionnaire, and somewhere between the insurance questions and the modern slavery statement is a new line: "Please provide your Scope 1, 2 and 3 emissions for the last financial year."

For many small and mid-sized businesses, that is the first time anyone has asked. It will not be the last.

Why the question keeps coming up

Most UK SMEs are not legally required to report their emissions. But the organisations they sell to increasingly are, and they need numbers from their suppliers to complete their own reports.

• Big customers. Large UK companies and LLPs report energy use and emissions under Streamlined Energy and Carbon Reporting (SECR). Many also set net zero targets, and most of their footprint sits in their supply chain (their Scope 3). Your emissions are part of their emissions.
• Public sector tenders. Suppliers bidding for central government contracts worth more than £5 million a year must publish a Carbon Reduction Plan under PPN 006 (which replaced PPN 06/21 in February 2025). NHS England asks its suppliers for carbon reduction plans or net zero commitments too, and these expectations flow down to subcontractors.
• Importers. The UK Carbon Border Adjustment Mechanism (CBAM) starts on 1 January 2027, about two months from now. It covers imports of aluminium, cement, fertiliser, hydrogen, and iron and steel, and importers will need emissions data from their suppliers.
• Lenders and investors. Banks are measuring the emissions linked to their lending, and some now ask business customers for carbon data.

The result is simple: having a credible carbon footprint is becoming part of winning and keeping work.

What a good answer looks like

You do not need a 60-page sustainability report. Most customers want four things:

1. Your total emissions in tonnes of CO2e, split into Scope 1, 2 and 3.
2. A clear method. Ideally the GHG Protocol, using the UK government's published conversion factors.
3. A reporting period and boundary. Which year, and which sites or companies are included.
4. A plan. A target, and what you are doing to reduce your emissions.

The three scopes in plain English

• Scope 1: emissions you create directly, such as gas boilers, company vehicles and refrigerant leaks.
• Scope 2: emissions from the electricity, heat or steam you buy.
• Scope 3: everything else in your value chain, such as purchased goods, transport, business travel, commuting and waste. It is usually the biggest share, and the hardest to measure.

Five steps to your first footprint

1. Pick your year. Use your last financial year, so the numbers line up with your accounts.
2. Gather the easy data first. Energy bills, fuel cards and mileage claims cover most of Scope 1 and 2.
3. Estimate Scope 3 sensibly. Start with spend-based estimates from your purchase ledger, then replace the biggest items with real data from suppliers over time.
4. Apply recognised conversion factors. The UK government publishes these every year. Write down which ones you used.
5. Set a target and a few actions. Customers care as much about direction of travel as the starting number.

The first footprint will not be perfect, and that is fine. What matters is that it is honest, repeatable and clearly explained. Accuracy improves each year.

Common mistakes to avoid

• Leaving out Scope 3. Customers can see when a footprint is too small to be believable.
• Mixing up years or sites. Keep a clear boundary and stick to it.
• Not keeping the evidence. If a customer or auditor asks how you got a number, you should be able to show them.
• Treating it as a one-off. The same questions will come back every year, often from more customers.

How GreenThread helps

GreenThread is DMG's carbon accounting software for UK organisations. It helps you measure your footprint, cut it and prove it, without needing a sustainability team.

• Scope 1, 2 and 3 in line with the GHG Protocol, including all 15 Scope 3 categories
• Built-in conversion factors, including the UK government factors
• AI bill reading that pulls energy and fuel data straight from your invoices
• Supplier data requests, so you can replace estimates with real numbers
• Targets and reduction plans to show customers where you are heading
• Reports for customers and tenders, with the evidence behind every figure

Plans start at £49 a month, with a 14-day free trial.

Start your free trial of GreenThread

This article is general information, not legal, tax or assurance advice. Always check the official guidance that applies to your organisation.