Fleet decarbonisation in the UK: ZEV mandate, carbon reporting and a practical 2026 roadmap

Fleet decarbonisation in the UK is driven by three forces rather than one law. The ZEV mandate forces manufacturers to sell a rising share of zero-emission cars and vans, so the market tilts towards electric. Carbon reporting (SECR for large companies, carbon reduction plans for public contracts) makes fleet emissions visible. And tax (4 % company car tax on electric cars, nil van benefit charge, road tax changes) makes the business case.

No UK rule obliges a private company to electrify its fleet by a given date. But if you report under SECR, bid for central government contracts, or supply a customer with net zero targets, your company cars and grey fleet are already on the scorecard. This guide covers the rules that apply to you, how to measure fleet emissions with the 2026 government factors, and a six-step roadmap with a worked example. At Voltaback, we see the same sticking point in most fleets: the plan exists, but the data to prove progress does not.

Which rules apply to your fleet in 2026?

The rest of this guide takes each line in turn.

The ZEV mandate: why it matters to a fleet that is not bound by it

The ZEV mandate sets the minimum share of each manufacturer's new car and van sales in the UK that must be zero emission at the tailpipe. Manufacturers that miss it must buy credits from others or pay a compliance payment per missing vehicle. Fleets have no quota, but they buy in the market the mandate shapes.

Until 2029, manufacturers can meet these headline targets partly through flexibilities (borrowing, credit transfers between cars and vans, CO2 savings on non-ZEV models). These flexibilities were widened in April 2025 and again in early 2026, when compliance payments were also reduced. Source: GOV.UK, ZEV mandate review consultation, August 2026.

2030, 2035 and the 2026 review

• 2030: end of sales of new cars powered only by petrol or diesel.
• 2030 to 2035: full hybrids and plug-in hybrids can still be sold new.
• 2035: all new cars and vans zero emission.

In August 2026 the government opened a review of the annual targets, which closed on 23 October 2026. It states that the 2030 and 2035 end goals are not changing; the interim pathway may. Source: GOV.UK, review launched to shape pathway to 2035.

What this means for your fleet: a car leased in 2026 on a four-year contract comes back in 2030, when its replacement will in practice be electric or hybrid. Battery electric cars already made up about 26 % of new car registrations in the first nine months of 2026, according to SMMT figures reported by electrive. Fleets and businesses account for most new car registrations, so the transition largely runs through company car policies.

Carbon reporting: SECR, scope 1, 2 and 3 for company cars

Who must report under SECR

Streamlined Energy and Carbon Reporting has applied since April 2019 under the Companies (Directors' Report) and Limited Liability Partnerships (Energy and Carbon Report) Regulations 2018. It covers:

• quoted companies, which report global energy use and emissions;
• large unquoted companies and large LLPs, meaning those that meet at least two of the Companies Act 2006 size criteria: turnover, balance sheet total, and 250 employees or more. The turnover and balance sheet limits were raised from April 2025 (to £54 million and £27 million for the medium-company ceiling), so check your classification with your auditor;
• with an exemption for low energy users that consumed 40 MWh or less in the UK over the period.

Source: GOV.UK, environmental reporting guidelines including SECR.

What a large unquoted company must disclose

• UK energy use, including transport fuel and electricity, in kWh;
• the related greenhouse gas emissions;
• at least one intensity ratio (for example tCO2e per £m of turnover, or per employee);
• the energy efficiency actions taken in the year;
• the methodology used.

Where each type of car sits

The SECR guidance states that large unquoted companies and LLPs must disclose energy and emissions from business travel in rental cars or employee-owned vehicles where they are responsible for purchasing the fuel. Grey fleet is therefore not optional for most SECR reporters. Sources: GOV.UK SECR guidance (PDF), Energy Saving Trust fleet decarbonisation toolkit.

UK SRS: the next layer

The UK Sustainability Reporting Standards (UK SRS S1 and S2), the UK versions of the ISSB standards, were published in February 2026 for voluntary use. Any mandatory requirement would come through later legislation, and the government has said it will review how UK SRS fits with SECR. Source: ICAEW, UK Sustainability Reporting Standards. For fleets, the practical message is the same: scope 3 data, including grey fleet, will be asked for more often, not less.

Public contracts and supply chains: PPN 006 and the government fleet

PPN 006 carbon reduction plans

Under the Procurement Act 2023, Procurement Policy Note 006 (which replaced PPN 06/21 for procurements started from 24 February 2025) asks central government departments, their executive agencies and non-departmental public bodies to require a Carbon Reduction Plan from bidders on contracts worth more than £5 million a year (including VAT), where relevant and proportionate.

The plan must:

• confirm a commitment to net zero by 2050 for UK operations;
• report current scope 1 and 2 emissions and a defined subset of scope 3, which includes business travel and employee commuting;
• set out baseline emissions, reduction targets and measures, with board sign-off;
• be published on the supplier's website and updated at least annually.

Source: GOV.UK, PPN 006 carbon reduction plans. The NHS applies its own carbon reduction plan requirement to its suppliers: NHS England.

For a service company with technicians, sales staff or engineers on the road, company cars and grey fleet are often the largest line in scope 1 and business travel. A credible plan to electrify them is one of the quickest wins in a CRP.

Greening Government Commitments

Central government set itself a target of 100 % of its car and van fleet fully zero emission by 31 December 2027, after reaching 25 % ultra-low emission cars by the end of 2022. Source: GOV.UK, government fleet commitment. Departments increasingly expect the same direction from their suppliers.

How to measure your fleet's emissions with the 2026 government factors

The UK government publishes greenhouse gas conversion factors every year for company reporting. The 2026 factors for an average car:

The factors also give an energy figure for SECR: 0.32763 kWh per mile for an average battery electric car. Source: GOV.UK greenhouse gas reporting conversion factors 2026.

Two practical points:

• Per mile or per kWh: per mile factors are averages. If you know the real kWh each car charged, multiplying by the electricity factor gives a more accurate figure, and a more defensible one.
• Plug-in hybrids: the factor assumes an average share of electric driving. A hybrid that is rarely plugged in emits close to a petrol car. Only real fuel and charging data shows the difference.

Worked example: a 150-car fleet

A company runs 150 cars averaging 15,000 miles a year: 110 diesel, 25 plug-in hybrids, 15 battery electric.

Moving the whole fleet to electric cuts its emissions by about 82 % on the 2026 factors, and the figure improves each year as the grid decarbonises. With a four-year replacement cycle and an electric-only policy from 2027, most of that reduction lands by 2030.

A six-step roadmap to decarbonise a UK fleet

Step 1: audit the fleet and the grey fleet

List every vehicle: owned, leased, salary sacrifice, pool cars, vans, and employees' own cars used for business. For each, capture real annual mileage, fuel or energy used, contract end date and the driver's charging options at home. The grey fleet is often the largest blind spot, and under SECR it may already be reportable.

Step 2: set a car policy with dates

• Electric only for new orders from a set date, with documented exceptions (very high mileage, towing, no charging access).
• Plug-in hybrids only by exception, with a requirement to charge and a check on real electric miles.
• A list price cap that reflects the £50,000 threshold of the expensive car supplement on VED.
• A grey fleet rule: minimum standards for own cars, and a route into a company or salary sacrifice EV.

Step 3: plan charging for each driver

• Home charging covers most company car drivers' daily needs. Our guide to reimbursing home charging sets out the methods.
• Workplace charging for drivers without a driveway and for pool cars, sized on dwell time rather than peak power.
• Public charging through a fuel card or a charging card for long trips.

Step 4: get the money flows right

HMRC allows an employer to repay all the electricity used to charge a company car at home, private miles included, with no tax and no National Insurance. Source: HMRC Employment Income Manual EIM23900. If drivers are under-repaid, they lose money on every charge and adoption stalls. If they are over-repaid on a flat rate, the cost of the fleet rises quietly. To estimate this line for your fleet, use the home charging cost calculator.

Step 5: support the drivers

Training on charging, a clear policy document, and eco-driving coaching reduce range anxiety and energy use. Our article on eco-driving for fleets shows what it saves per driver.

Step 6: measure, report and adjust

Track four indicators each quarter: share of electric cars in the fleet, share of electric cars in new orders, real tCO2e per mile, and real electric share of plug-in hybrids. Feed them into SECR, your carbon reduction plan and customer questionnaires.

A realistic calendar for a fleet on four-year leases

The calendar follows contract end dates, so no car is replaced early and no early termination fee is paid. The pace is set by the policy date in April 2027: every order after it is electric, and the fleet turns over by itself.

Roadmap checklist

• Fleet and grey fleet inventory with real mileage
• Car policy signed off, with dates and exceptions
• Home charging set-up and reimbursement method for each driver
• Workplace charging plan and grant check
• Driver communication and training
• Quarterly emissions report using the current government factors

Plug-in hybrids: the weak point of many UK fleets

Plug-in hybrids were the bridge choice of many company car policies because of their low company car tax. Three changes now weaken that case:

• their company car tax is far higher than that of a battery electric car;
• from April 2028, they will pay 1.5p per mile of eVED on top of fuel duty;
• their emissions in your report depend on how often they are plugged in, which many fleets do not know.

The quickest win in many fleets is to measure the real electric share of each plug-in hybrid, then move the low-share drivers to a battery electric car at the next renewal.

The TCO levers that pay for the transition

Decarbonisation is cheapest when it follows the replacement cycle and when every cost line is counted:

• Company car tax: 4 % of list price for electric cars in 2026/27, against far higher percentages for petrol and diesel cars. The detail is in our guide to electric company car tax benefits.
• Road tax: £200 a year standard VED for all recent cars, a supplement above £50,000 for electric cars, and eVED at 3p per mile from 2028. See road tax on electric cars.
• Vans: nil van benefit charge for zero-emission vans.
• Energy: home charging on an off-peak tariff costs a fraction of public rapid charging. This is the line that varies most between fleets.

Put together, these lines usually make an electric company car cheaper per mile than a petrol one over the contract, as our electric vs petrol company car TCO shows.

Proving progress: the data a carbon report needs

A decarbonisation plan is judged on data, not intentions. For each car you need real mileage and real energy: kWh charged at home, at work and on the road, and fuel for the remaining combustion cars. Without it, reports fall back on averages and declared mileage, which auditors and procurement teams increasingly question.

Voltaback provides this data without hardware: mileage, consumption and home charging sessions read from the car's connected services, for more than 48 brands. Each home session is valued at the driver's real tariff and repaid through a monthly statement. Voltaback relies on the home's MID-certified meter, not on a standalone cable meter, and the measurement is audited by an independent third party at 1.22 % average relative error. The company never receives drivers' geolocation. The platform is ISO 27001 certified and UK GDPR compliant.

What fleet managers do with it is set out on our fleet manager page.

From plan to proof

The UK rules leave you free to choose your pace, but carbon reporting, public buyers and the tax system all point in the same direction. The fleets that move fastest are those that sort out charging and reimbursement early and can show real data at the end of each year.

Book a 30 minute demo to see how Voltaback measures home charging and mileage across your fleet, without hardware, and turns them into the figures your carbon report needs.