Take a mid-sized Sheffield precision manufacturer with £48 million turnover and a total footprint of 2,400 tonnes CO2e. Their supply chain screening shows scope 3 at 1,845 tonnes. Because that share exceeds the 40 percent threshold under the Science Based Targets initiative, they must now cover two-thirds of that category in any validated target. Two-thirds of 1,845 is 1,230 tonnes.
The supplier engagement letter for scope 3 data does not need to reach all 128 tier-one vendors. It needs to reach the subset responsible for 1,230 tonnes. In this illustrative example, that means the top eleven suppliers by emissions contribution. Everything else is noise.
Illustrative example assumptions: spend correlates with emissions, suppliers are tier-one only, and the 2,400 tonne total excludes biogenic carbon.
“Our suppliers will just ignore another questionnaire.”
They won’t ignore it if it arrives from someone they already invoice. The mistake most firms make is treating supplier data collection like a customer satisfaction survey. It’s not. It’s a procurement discipline. A well-written supplier engagement letter for scope 3 data should come from a known category manager, reference an existing contract, and give a clear deadline.
According to the GHG Protocol Corporate Standard, scope 3 covers fifteen categories, but for most UK SMEs, purchased goods and services dominates. You don’t need a lifecycle assessment from every firm. You need a number, a method, and a date. If the letter asks for those three things and nothing else, response rates jump. When suppliers do reply, the data is often patchy. That’s fine. Your first letter is reconnaissance, not an audit.
Here’s the contrarian view: some suppliers will ignore you. That’s acceptable. If you’re chasing a 100 percent response rate, you’re optimising for vanity, not coverage. A 60 percent response rate that captures 85 percent of your spend-based emissions is infinitely more useful than 95 percent of suppliers confirming they haven’t measured anything yet.
“We are only an SME. Our suppliers are even smaller.”
Size is irrelevant to physics. A small supplier shipping you steel still carries the embodied carbon of that steel. The UK Government SECR guidance already expects quoted companies to report scope 3 where material, and the ripples of CSRD are hitting UK SMEs through large corporate customers. If you are supplying a FTSE 250 firm, their data request is coming whether you are ready or not.
Smaller suppliers often respond faster than large ones. They have one factory, one energy bill, and one managing director who answers emails personally. The supplier engagement letter for scope 3 data should reflect that simplicity. Ask for total annual electricity and gas usage, not a full carbon accounting exercise. Keep the tone collaborative. Mention that you are happy to share your own methodology or introduce them to your auditor.
The pushback we hear on calls is that small suppliers fear exposure. They worry you will use the data against them in negotiations. That rarely happens in practice, but the fear is real. Address it head-on: state explicitly that the data is for reporting only and will not feed into commercial scorecards.
“The supplier engagement letter for scope 3 data is procurement’s job, not ours.”
Who should own the letter? Procurement or sustainability? Neither, on their own. Procurement owns the relationship, but sustainability owns the methodology. If procurement writes the letter alone, they often strip out the technical language because they worry about sounding difficult. If finance writes it alone, it lands cold. The best versions are co-signed by both, or drafted by sustainability and sent via procurement’s mailbox.
When we run auditing supply chain emissions engagements, the first thing we check is who sent the previous request. If it came from a generic “sustainability@” address, we know why the response rate sits below 20 percent. We have seen the best results when the sustainability team drafts three template versions and procurement picks the one that matches their relationship style.
The uncomfortable truth is that neither department really wants ownership. Procurement fears damaging rapport; sustainability fears looking commercially naive. Our advice is to put procurement’s name on the envelope and sustainability’s phone number in the footer. That splits the social cost.
“We will get fifty different formats back and none of it will match our accounting.”
You will. That is why you standardise the ask, not the response. Your supplier engagement letter for scope 3 data should include a one-page template that maps directly to your greenhouse gas protocol scopes categories. Ask for the same reporting year, the same unit, and the same boundary.
Even then, you will receive spreadsheets in kilowatt-hours, PDFs in kilograms CO2e, and emails that simply say “we are green.” The trick is to tier your expectations.
| Collection method | Best for | Typical response rate | Data quality | Your effort |
|---|---|---|---|---|
| Templated letter + Excel | First outreach to tier-one suppliers | 25-40% | Low to medium | High (manual chasing) |
| Online survey tool | Mid-size supplier lists | 35-50% | Medium | Medium |
| Carbon accounting platform | Ongoing annual collection | 60-80% | High | Low after setup |
The realist’s position is that imperfect data beats no data. If a supplier sends a corporate-level figure rather than product-level, allocate it by spend and move on. You can refine it next year. Carbon accounting spreadsheet versus software debates often miss the point: the bottleneck is supplier willingness, not your tool. Start with the template approach. It builds internal discipline before you spend money on software.
“SECR does not even require scope 3 reporting, so why rush?”
SECR doesn’t mandate scope 3 for unquoted large companies or LLPs, but it explicitly encourages it where material. More importantly, SBTi and CDP both require it, and your customers are increasingly asking for it in tender pre-qualification questionnaires. If you are planning to set science based targets as an SME, scope 3 is not optional once it crosses that 40 percent line.
Waiting for a mandate is a terrible strategy. Good scope 3 data takes eighteen months to mature. You need one year to collect, six months to clean, and another cycle to verify trends. The supplier engagement letter for scope 3 data you send today is not for this year’s report. It is for the baseline you will rely on in 2027. By the time scope 3 becomes mandatory under UK law, the firms that started in 2024 will have three years of trend data. That is what separates a credible net zero claim from a guess.
On client calls, we often hear: “We will wait until the regulation forces our hand.” That is a choice. But remember, your competitors are already collecting this data and using it to win contracts that require supply chain transparency. Regulation is a floor, not a ceiling.
“We have sent the letter. Nothing happened.”
Expect silence. Then follow up. We recommend a three-touch sequence: initial letter, reminder at ten working days, and a final nudge at twenty days. The third touch should come from procurement, not sustainability, and it should mention the commercial relationship explicitly. Not as a threat, but as context.
If a supplier still does not reply, model their emissions using your spend data and a DEFRA or GHG Protocol emission factor. Flag it as a proxy in your inventory and target them again next year. Over time, the share of modelled data should shrink. Set a calendar reminder for month eleven. If they haven’t responded by then, they have self-selected out of your primary data set.
Here is the caveat: do not let perfect coverage become the enemy of a good baseline. One client spent eight months chasing a single vendor that contributed 0.3 percent of their scope 3. That is eight months of delay for vanity. Cut them off at three attempts, model them, and redirect your energy to the top ten.
If you have drafted a letter and are unsure whether it asks for the right data, send it to us and we will review it without charge.
The supplier engagement letter for scope 3 data is not a legal instrument. It is a conversation starter. And like most conversations in business, the ones that matter are brief, specific, and slightly uncomfortable. If your letter feels too polite to refuse, it is probably also too vague to action.
Get in touch if you want help working out which eleven suppliers actually matter. We will run the numbers with you.
Frequently asked questions
Do I need to send a supplier engagement letter for scope 3 data to every supplier?
No. You should prioritise by emissions contribution, not supplier count. Start with the vendors that represent the top two-thirds of your scope 3 spend or emissions, then work downstream. Chasing a 100 percent response rate wastes time and annoys smaller suppliers who contribute less than one percent of your footprint.
What should the letter actually ask for?
Keep the first request modest. Ask for total corporate emissions, a relevant emission factor, or at minimum, energy and fuel data for the reporting year. Do not ask for full product lifecycle assessments in your first outreach. You are building a relationship, not auditing them.
My supplier says they do not have the data. What now?
Offer to accept spend-based estimates or industry averages as a placeholder. If they refuse entirely, model their emissions using your purchase data and an emission factor from DEFRA or the GHG Protocol. Document the proxy method and flag it for improvement next year.
How formal does the letter need to be?
It depends on the relationship. A signed PDF on letterhead works for strategic vendors. A well-written email from a known account manager is often enough for smaller firms. The key is that it comes from someone the supplier already trusts, not a generic sustainability mailbox.
