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Supplier sustainability assessment: what UK buyers check and how to prepare
A supplier sustainability assessment is how a customer checks your environmental, labour, ethics and purchasing practices before it buys from you, most often through EcoVadis or the NHS Evergreen assessment. You answer questions, upload evidence and receive a score or level that the buyer compares with its own threshold.
What is a supplier sustainability assessment?
Large buyers now count part of their suppliers' footprint as their own. A retailer's carbon target and a manufacturer's own EcoVadis score both depend in part on what its suppliers do. So before a contract, or at renewal, the buyer runs a supplier assessment and asks you to show your practices.
Most assessments follow the same pattern. You answer a questionnaire, upload policies and records, and an analyst or the buyer's procurement team turns them into a score. The result lasts about a year. Then the request comes back.
An assessment marks your evidence, not your intentions. A policy that exists but isn't signed, dated or applied usually scores the same as no policy at all.
Which assessments do UK buyers use?
Five come up most often for a UK supplier of 200 to 1,000 staff.
| Assessment | Who asks for it | What you get | How often |
|---|---|---|---|
| EcoVadis | Large private buyers in most sectors | A score out of 100 across four themes, with medals for the strongest | Every 12 months |
| NHS Evergreen | NHS trusts, NHS Supply Chain and NHS England medicines tenders | A maturity level from 1 to 4 | Every 12 months |
| CDP supply chain | Buyers who report to CDP themselves | A score from A to D- on climate, and on water or forests if asked | Yearly cycle |
| Sedex | Retail, food and consumer goods | A self-assessment questionnaire (SAQ), plus a SMETA ethical audit if the customer asks | SAQ kept up to date; audits as requested |
| The customer's own questionnaire | Almost everyone else, often through IntegrityNext, Achilles or a spreadsheet | A pass, a fail or an internal score | Varies |
The formats differ. The evidence underneath barely changes, which is the good news: one organised set of documents can answer all five.
If a customer has sent you a CDP request, see CDP for suppliers.
How does an EcoVadis assessment work?
EcoVadis is the assessment most UK suppliers meet first. Your customer sends an invitation, you register and choose a plan, and EcoVadis builds a questionnaire for your size, sector and country. Analysts then check your answers against the documents you upload and issue a scorecard out of 100.
It covers four themes: environment, labour and human rights, ethics, and sustainable procurement. For each, the analyst looks for policies, actions and results, and credits only what your documents prove. Our EcoVadis rating guide explains medals, costs and timings.
Deadline close? Our fast-track EcoVadis support gets you submitted in ten working days.
What is the NHS Evergreen assessment?
Evergreen is the NHS's own supplier sustainability assessment. It is free, runs on the Atamis procurement portal, and gives you a maturity level from 1 to 4 that lasts 12 months.
Level 1 asks for a public commitment to net zero by 2050, with emissions and a target covering Scope 1, Scope 2 and some of Scope 3 for your UK business. Level 2 adds all relevant Scope 3 emissions, a published modern slavery statement and a social value programme. Levels 3 and 4 need an independently validated 2045 target, and Level 4 also asks for a transparency rating such as CDP, EcoVadis or B Corp.
Most NHS buyers use Evergreen for information rather than to score bids. Two exceptions matter. NHS Supply Chain frameworks and NHS England medicines tenders require it, and recent NHS Supply Chain tenders ask for Level 1 achieved in the 12 months before the tender closes. Since 1 April 2026, the questions behind Level 1 must be answered before you can submit at all.
Our NHS Evergreen guide covers each level and how to reach it.
Why do good suppliers get low scores?
The same gaps cost points on every platform.
- Policies with no proof they work. Assessors want the training record or the board minute as well as the PDF.
- No numbers. Twelve months of energy, fuel and waste data turns "partly" into "yes" on most environmental questions.
- No target. A dated, public net zero commitment is the difference between Evergreen Level 1 and no level at all.
- Purchasing left blank. You are a buyer too. A supplier code of conduct, and a record of who accepted it, scores on EcoVadis and Sedex alike.
How do you answer a supplier sustainability questionnaire?
Treat it as an exam where the marks go to evidence. Answer only what you can prove, attach the document that proves it, and use the same numbers in every questionnaire you send back. Buyers compare answers year to year, and across platforms.
Most supplier sustainability questionnaires, whether EcoVadis, a customer's own ESG questionnaire or a tender section, ask about the same five things: your policies, your emissions, your targets, your actions and your results. Build one evidence pack that covers those five, and each new questionnaire becomes a copy-and-check job instead of a fresh project.
How do you prepare for a supplier sustainability assessment?
- List what's coming. Note every assessment your customers have sent or mentioned, with its deadline. Our guide to sustainability requirements for suppliers shows which ones apply to you.
- Check your gaps before the questionnaire opens. Score yourself honestly against the evidence each assessment wants. The free readiness check below does this in one sitting.
- Fill the biggest gaps first. Usually a signed environmental policy, a year of energy and emissions data, a net zero commitment and a supplier code of conduct.
- Keep one evidence base. Store each document once, with an owner and a review date, and point every assessment at it.
- Treat the scorecard as your plan. Each assessor lists your weak points. Fix them before the next cycle.
Suppliers who prepare once answer every request faster. Suppliers who start each questionnaire from a blank page pay for it every year.
What this could earn you. The same evidence puts energy, materials and waste costs side by side, often for the first time, and that is where savings tend to appear. A stronger score can also deliver competitive advantage in tenders where rivals have not done the work.
Train the people who answer. A short course in carbon literacy keeps sales, bids and operations giving the same answers, and the attendance record is evidence in its own right.
Common questions
What is a supplier sustainability self-assessment?
A questionnaire you complete about your own practices, without an assessor checking each answer. NHS Evergreen and the Sedex SAQ work this way. EcoVadis is different: analysts check your answers against your documents before they score you.
How long does an EcoVadis assessment take?
Plan on three to four months from registration to scorecard. The questionnaire window is 30 business days by default and can be extended. Most of the time goes on gathering evidence, so start that before you register.
Is the NHS Evergreen assessment mandatory?
Not for every NHS contract. NHS Supply Chain frameworks and NHS England medicines tenders require it, and recent NHS Supply Chain tenders ask for Level 1. Any supplier to the NHS in England can complete it free on Atamis.
Can one set of evidence answer every assessment?
Mostly. Policies, energy and emissions data, a supplier code of conduct and training records come up in nearly every questionnaire. Keep them in one place with an owner and most new requests become a matter of reformatting.
Need a hand with an assessment? See our EcoVadis consultant service and fixed fees, or our guide to sustainability requirements for suppliers.