Fleet Carbon Reporting UK: What You Need to Track and Why
Fleet vehicles are typically the largest single source of direct carbon emissions for businesses with a mobile workforce. Here's how to measure them, report them correctly, and build the data foundation to reduce them.
UK fleet carbon reporting sits at the intersection of regulation, commercial pressure, and genuine operational improvement. For quoted companies and large private businesses, Streamlined Energy and Carbon Reporting (SECR) makes fleet emissions disclosure a legal requirement. For the thousands of SMEs below the threshold, customer sustainability questionnaires, supply chain due diligence, and ESG lending criteria are creating de facto reporting pressure.
The good news: getting fleet carbon reporting right is more straightforward than it looks. The data you need — mileage, fuel consumption, vehicle type — should already exist in your fleet management system. The challenge is structuring it correctly, applying the right emission factors, and building a process that holds up to scrutiny year after year.
Who must report: SECR thresholds
The Streamlined Energy and Carbon Reporting (SECR) framework requires affected companies to disclose energy use and greenhouse gas emissions in their annual report.
| Company type | SECR obligation |
|---|---|
| Quoted companies (any size) | Full SECR: Scope 1, 2, intensity metric, reduction action narrative |
| Large unquoted companies (250+ employees or £36m+ turnover) | Full SECR: Scope 1, 2, intensity metric, reduction action narrative |
| Large LLPs (same thresholds) | Full SECR reporting required |
| Medium companies (50–249 employees) | No legal obligation, but customer/investor pressure growing |
| Small companies (<50 employees) | No legal obligation |
Source: Companies Act 2006 (Strategic Report and Directors' Report) Regulations 2013, as amended by The Companies (Directors' Report) and Limited Liability Partnerships (Energy and Carbon Report) Regulations 2018.
Scope 1, 2, and 3: what counts as fleet emissions?
Direct combustion emissions from fuel burned in your owned or controlled vehicles. Diesel, petrol, HVO, CNG. Required for SECR.
Indirect emissions from purchased electricity — including EV charging at your depots. Required for SECR alongside Scope 1.
All other indirect emissions: grey fleet, upstream fuel production, vehicle manufacturing. Voluntary for most, mandatory in some supply chains.
For most UK fleet managers, SECR compliance means accurately capturing Scope 1 fuel emissions and Scope 2 electricity for EV charging. Scope 3 grey fleet is increasingly requested but not yet universally mandatory. The most common gap in fleet carbon reports is grey fleet — business mileage in employee-owned vehicles is significant but routinely excluded.
8 steps to a robust fleet carbon report
Establish your reporting boundary
Decide which vehicles are in scope. Owned vehicles are clearly included. Leased vehicles (finance lease and operating lease) are typically included. Vehicles driven by employees on personal insurance for business (grey fleet) are Scope 3 and often excluded from basic reports but required for supply chain disclosure. Set your boundary before collecting data — changing it mid-year undermines comparability.
Collect mileage and fuel data
For Scope 1 emissions, you need total fuel consumed per vehicle per period, broken down by fuel type (diesel, petrol, HVO, CNG). If you don't have fuel card integration, use total mileage × fleet average mpg as an approximation. For EVs, you need total kWh from charging. Your fleet management system should be the primary source — manual fuel receipts are unreliable and auditor-unfriendly.
Apply DEFRA emission factors
DEFRA publishes annual emission conversion factors for greenhouse gas reporting. For 2024/25 reporting: diesel is approximately 2.52 kg CO2e/litre, petrol 2.31 kg CO2e/litre, and the UK grid electricity factor is approximately 0.207 kg CO2e/kWh. Always use the DEFRA factors from the year your emissions occurred — factors change annually as the energy mix evolves.
Calculate intensity metrics
Absolute CO2e tonnage is required for SECR, but intensity metrics — CO2e per mile, per £ revenue, or per vehicle — tell a more useful management story. Intensity metrics allow year-on-year comparison that adjusts for fleet growth or contraction. They are also the basis for fleet decarbonisation target-setting.
Document grey fleet
Grey fleet — employee-owned vehicles used for business journeys — is consistently under-reported and is a blind spot for organisations with a large field workforce. Mileage expense claims are your primary data source. Apply the DEFRA per-mile emission factors for private cars by engine type. Grey fleet emissions can be surprisingly significant for professional services and healthcare organisations.
Include EV charging
Battery electric vehicles have zero Scope 1 emissions, but grid electricity charging creates Scope 2 emissions. For home charging (drivers charging at home), use the DEFRA domestic electricity factor multiplied by estimated business kWh consumed. For depot charging, use your actual electricity consumption. Consider renewable energy certificates (REGOs) if your organisation purchases certified green electricity — these can reduce your Scope 2 figure to near zero.
Set a baseline and targets
A one-year snapshot has limited value. Establish a baseline year (typically the year before your decarbonisation programme began) and track absolute emissions and intensity metrics annually against it. The UK government's net zero target requires substantial fleet emissions reductions by 2035 (the phase-out of new petrol/diesel cars) and 2040 (vans). Build your fleet replacement schedule around these milestones.
Prepare for supply chain disclosure
Large enterprise customers increasingly require suppliers to disclose Scope 1 and 3 emissions in tender responses and contract renewals. The CDP supply chain programme, customer sustainability questionnaires, and finance institution ESG due diligence are all moving in this direction. A defensible, annually-verified fleet carbon figure positions your business well in competitive procurement contexts.
DEFRA emission factors: quick reference (2024/25)
Always use the official DEFRA publication for the reporting year in question. Factors below are indicative and based on 2024 DEFRA guidelines.
| Fuel / energy type | Unit | kg CO2e |
|---|---|---|
| Diesel (market-based) | per litre | 2.52 kg CO2e |
| Petrol (market-based) | per litre | 2.31 kg CO2e |
| Hydrotreated vegetable oil (HVO) | per litre | 0.19 kg CO2e |
| UK grid electricity | per kWh | 0.207 kg CO2e |
| Average petrol car (per mile) | per mile | 0.170 kg CO2e |
| Average diesel car (per mile) | per mile | 0.168 kg CO2e |
| Average diesel van (per mile) | per mile | 0.198 kg CO2e |
Indicative only. Always reference official DEFRA conversion factors for your reporting period.
How FleetGS supports fleet carbon reporting
A defensible fleet carbon report starts with accurate mileage and fuel data. FleetGS captures vehicle mileage per trip, per driver, and per vehicle — and exports in formats that work directly with DEFRA emission factor spreadsheets.
Mileage reporting by vehicle and driver
Export total business miles per vehicle and per driver for any date range — the foundation of both Scope 1 and grey fleet calculation.
Fuel consumption tracking
Log fuel fills manually or via fuel card integration. FleetGS tracks litres consumed by fuel type, the key input for Scope 1 CO2e calculation.
Route history export
90 days of GPS route history per vehicle, exportable for audit verification of mileage figures.
EV mileage separation
Tag vehicles as EV or ICE and report mileage separately — essential for calculating Scope 1 (ICE) and Scope 2 (EV charging) emissions correctly.
For the wider picture of fleet cost and efficiency, see our guides on reducing fleet costs, managing an electric vehicle fleet, and FleetGS reporting features.
Frequently asked questions
It depends on your company size. Quoted companies, large private companies (250+ employees or £36m+ turnover), and LLPs meeting similar thresholds must report Scope 1 and 2 greenhouse gas emissions under SECR (Streamlined Energy and Carbon Reporting). Smaller companies have no mandatory reporting obligation, but fleet carbon data is increasingly required by customers, insurers, and lenders as part of supply chain due diligence.
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