Why Scope 3 Is Where Most CRPs Fall Short
When UK SMEs first produce a Carbon Reduction Plan for a public sector tender, the instinct is to focus on what is easy to measure. Scope 1 covers direct emissions from gas boilers and company vehicles. Scope 2 covers purchased electricity. These figures are available from utility bills, and most businesses can produce a credible estimate within a few hours.
Scope 3 is different. It covers all indirect emissions in a company value chain, upstream and downstream, that are not owned or directly controlled by the organisation. Under the GHG Protocol Corporate Value Chain Standard, there are 15 separate categories of Scope 3 emissions. For a typical UK SME, several of these categories will be immaterial or zero. But several will be highly material, and omitting them without explanation creates a gap that evaluators will notice.
PPN 006 does not require a perfect Scope 3 inventory. It does require a credible one. The guidance acknowledges that Scope 3 data is harder to obtain and allows for reasonable estimates based on available information. What it does not excuse is a CRP that treats Scope 3 as optional or lists a single token category to tick a box.
The 15 GHG Protocol Scope 3 Categories
The full list of Scope 3 categories under the GHG Protocol is as follows:
- Category 1: Purchased goods and services
- Category 2: Capital goods
- Category 3: Fuel and energy-related activities (not included in Scope 1 or 2)
- Category 4: Upstream transportation and distribution
- Category 5: Waste generated in operations
- Category 6: Business travel
- Category 7: Employee commuting
- Category 8: Upstream leased assets
- Category 9: Downstream transportation and distribution
- Category 10: Processing of sold products
- Category 11: Use of sold products
- Category 12: End-of-life treatment of sold products
- Category 13: Downstream leased assets
- Category 14: Franchises
- Category 15: Investments
For a professional services SME with ten employees, Categories 9 through 15 will typically be zero or negligible. For a product manufacturer or distributor, Categories 9, 11, and 12 may be significant. The key discipline is working through the list systematically, noting which categories apply to your business model, and providing a figure or a justified exclusion for each one that does.
The Categories Most UK SMEs Miss
In practice, the categories that appear most often in incomplete CRPs are the following.
Category 6 (Business travel) is frequently underreported because it relies on individual-level data that many SMEs do not collect systematically. Rail travel, flights, taxis, and hotel stays all have associated emissions. The HMRC mileage rate captures reimbursement cost, not carbon output. If your staff travel regularly by train or air and your CRP shows zero for business travel, that is a credibility problem. DEFRA publishes emission factors for rail, domestic flights, and major long-haul routes. Even rough estimates based on annual travel spend, combined with average cost-per-kilometre assumptions, produce a figure that demonstrates engagement with the issue.
Category 7 (Employee commuting) is similar. Many SMEs overlook it entirely on the grounds that they do not control how employees travel to work. That is correct from an operational standpoint, but the GHG Protocol includes it in Scope 3 because the emissions exist and are associated with the employment relationship. A headcount-based estimate using average UK commute data is acceptable. The DEFRA emission factors workbook includes commuting guidance.
Category 5 (Waste generated in operations) is often listed as negligible without any supporting calculation. For most office-based SMEs, operational waste is genuinely small. But the category includes waste sent to landfill, recycling, and incineration, all of which have distinct emission factors. A brief note explaining the basis for your estimate, even if the figure is small, demonstrates rigour.
Category 4 (Upstream transportation and distribution) catches out SMEs that purchase physical goods or materials. If your suppliers are shipping products to you by road or sea, those transport emissions sit in your Scope 3 inventory. Spend-based estimation using DEFRA or EEIO factors is the standard approach for SMEs that do not have activity-level data from their suppliers.
Category 1: The Hardest and Most Significant
Category 1, purchased goods and services, is typically the largest Scope 3 category for most organisations and also the hardest to quantify. It covers the full life-cycle emissions embedded in everything your business buys: IT equipment, office supplies, professional services subcontracted, software licences, marketing materials, and every other input to your operations.
For large organisations with mature sustainability functions, spend-based emission factors applied to procurement categories provide a reasonable estimate. For an SME without a dedicated sustainability resource, this calculation can feel overwhelming. The temptation is to omit it entirely.
Omitting Category 1 without explanation is the most common substantive weakness in SME Carbon Reduction Plans. Evaluators who understand the GHG Protocol will notice immediately. A credible approach for an SME is to apply DEFRA or the UK Government spend-based emission factors to your annual expenditure across two or three major spend categories, note the methodology used, and acknowledge that the figure is an estimate subject to improvement as supplier data becomes available. This demonstrates awareness and good faith without requiring a full lifecycle assessment.
Some supplier categories carry higher embedded emissions than others. IT hardware, for instance, has high embedded carbon relative to its cost. Professional services are generally lower. Grouping your major spend categories and applying appropriate factors is a proportionate approach that PPN 006 accommodates.
What "Reasonable Estimate" Means Under PPN 006
PPN 006 uses the phrase "reasonable estimate" specifically to give SMEs a workable path through Scope 3. It does not demand primary data from every supplier. It does not require a third-party verified inventory. What it requires is that you have engaged with the relevant categories, used a recognised methodology, and documented your assumptions.
Recognised methodologies for UK SMEs include the DEFRA Environmental Reporting Guidelines and the associated emission factors workbook, the GHG Protocol Corporate Value Chain Standard, and the EEIO (Environmentally Extended Input-Output) spend-based factors published by the UK Government. Any of these is acceptable. Using multiple approaches for different categories is also fine, as long as you note which methodology applies to which category.
The critical phrase is "documented your assumptions." An evaluator cannot assess a CRP that contains a single Scope 3 figure with no explanation of how it was derived. A CRP that says "Scope 3 emissions are estimated at 45 tonnes CO2e based on DEFRA spend-based factors applied to purchased goods and services (Category 1) and business travel (Category 6); other categories assessed as immaterial for our business model" is credible. A CRP that says "Scope 3: 45 tCO2e" with nothing else is not.
How CarbonVerified Handles Scope 3
CarbonVerified guides users through the most material Scope 3 categories for their specific business type. Rather than presenting all 15 categories as equally relevant, the platform uses your industry sector and a short operational profile to identify which categories are likely to be significant. You are then walked through the data inputs needed for each relevant category, with DEFRA-aligned emission factors applied automatically.
The output includes a documented methodology statement for each category, which is exactly what evaluators and auditors need to see. Categories assessed as immaterial are noted with a brief justification, so your CRP shows a complete and considered inventory rather than a selective one.
For Category 1 in particular, CarbonVerified uses a spend-based approach with UK Government EEIO factors, grouped by expenditure category. You input your annual spend in each category and the platform calculates the associated emissions estimate. It is not perfect data, and the platform says so clearly in the output, but it is a credible, documented, methodology-backed estimate. That is what PPN 006 asks for.
The Practical Priority Order
If you are reviewing your Scope 3 inventory and need to know where to focus first, the priority order for most UK service-sector SMEs is as follows. Start with Category 1 (purchased goods and services), because it is typically the largest category and the one most likely to be missing. Then address Category 6 (business travel) and Category 7 (employee commuting), because the data is accessible and evaluators will expect to see them. Then cover Category 5 (waste) and Category 4 (upstream transport) if relevant to your operations. For each category you assess as immaterial, note the reason briefly.
A Carbon Reduction Plan that takes this approach will be substantially more credible than one that either ignores Scope 3 or includes a single figure with no supporting detail. In a competitive tender, that credibility is worth protecting.
