If you have looked at a plug-in hybrid quote recently and the CO2 figure looked wrong, it probably was not. Official CO2 numbers for plug-in hybrids have risen sharply, in some cases by a factor of three, and the cars themselves have not changed at all.
What changed is the sum. Every plug-in hybrid's official CO2 figure is a blend of its petrol consumption and its electric running, weighted by something called the utility factor: the share of miles the test assumes you will cover on battery power. Regulators decided that assumption was too generous, so they rewrote it. The engine, the battery and the electric range are untouched. The number on the paperwork is not.
For a leasing customer this matters in one place above all others, which is company car tax. Here is what has happened, where Great Britain currently sits, and what to check before you sign anything.
What the Utility Factor Actually Does
A plug-in hybrid has two ways of covering a mile, and its official CO2 figure has to guess how often you use each one. The utility factor is that guess. A car with a long electric range gets a high utility factor, which means the test assumes most of its miles are electric, which drags the blended CO2 figure down towards zero.
The original utility factor was built on an optimistic view of how often drivers plug in. The Department for Transport's own estimate is that real-world CO2 from plug-in hybrids runs 243% above the WLTP figure. Euro 6e-bis rewrites the utility factor to narrow that gap, and a second revision tightens it again.
Nothing about this is a change to the car. A plug-in hybrid re-tested under the new factor has the same battery, the same range and the same fuel consumption in both modes. Only the weighting moved.
How Big the Change Is
The DfT published worked examples when it set out the case for adopting the new standard. They show the pattern clearly: the lower the starting figure, the larger the multiple.
| Old CO2 figure | Electric range | New figure |
|---|---|---|
| 10 g/km | 80 km | 30 g/km |
| 10 g/km | 120 km | 40 g/km |
| 30 g/km | 40 km | 60 g/km |
| 30 g/km | 80 km | 90 g/km |
You can see the result on manufacturers' own pages already. BMW's UK technical data for the X3 30e xDrive lists 64 to 68 g/km against a 19.7kWh battery and 52 to 54 miles of electric range. That is a plug-in hybrid with more than fifty miles of electric capability quoting a figure well above 50 g/km, which until recently would have been unthinkable on a car of that specification.
If you are comparing a re-homologated plug-in hybrid against one still quoting its older figure, you are not comparing two cars. You are comparing two test methods. Ask for both cars' CO2 to be confirmed in writing against the exact derivative on the quote before you draw any conclusion about which is cleaner.
Where Great Britain Sits Right Now
This is the part most coverage gets muddled, so it is worth being precise about what is settled and what is not.
| Position | |
|---|---|
| European Union | Euro 6e-bis applied to newly launched plug-in hybrids from 1 January 2025, and to models already on sale by the end of 2025. Existing models had to be re-homologated |
| Great Britain | The minimum emissions standard here is still Euro 6d. Adoption of Euro 6e-bis has been the subject of government consultation rather than settled law |
| Registered cars | HM Treasury has said there will be no retrospective changes to CO2 values for vehicles already registered |
| Next step | A further revision of the utility factor is expected to tighten figures again, which would affect cars type-approved after it takes effect |
A number of dates are circulating, including an April 2026 start with a transition running to April 2028, and retrospective application in Northern Ireland from January 2025. We have not been able to verify those dates against the published legislation, so we are not going to repeat them as fact. What is verifiable is that manufacturers are already publishing higher figures, and that the figure on your quote is the one your tax will be based on.
That last point is the practical one. Whatever happens to the standard, your benefit-in-kind charge is calculated from the CO2 figure recorded against your car at registration. Bands and rates change each tax year, so a car ordered now and delivered next year needs its figure confirmed rather than assumed.
What It Does to a Company Car Bill
Plug-in hybrids have been attractive as company cars for one reason: the bands below 50 g/km are very low, and a car that slipped under that line cost its driver a fraction of what an equivalent petrol SUV did.
Crossing 50 g/km is therefore not a small step. It moves a car out of the low plug-in hybrid bands and into a materially higher one, and because benefit-in-kind is a percentage of list price, the effect on an expensive SUV is not marginal. A driver comparing a plug-in hybrid now against the same model a colleague took two years ago can find the monthly tax has more than doubled on an identical car.
Two things follow. First, the case for a fully electric company car has strengthened, because its 0 to 3% treatment is unaffected by any of this. Second, if a plug-in hybrid still suits your mileage pattern, the comparison has to be run on the new figure, not on what plug-in hybrids used to cost. We are not tax advisers and a published band is not advice on your own position, so take the numbers to your accountant or payroll team before you commit.
Does Any of This Change Which Car You Should Lease?
For a private customer on a personal lease, almost not at all. You are not paying benefit-in-kind, and the first-year VED rate for a car in the 50 to 75 g/km range is higher than for one under 50, but it is a one-off that is usually built into the rental anyway. Your running costs depend on how often you actually charge, which no test method changes.
For a business driver it changes a great deal, and it changes it in favour of cars at either end rather than in the middle. A full electric car is unaffected. A petrol or diesel was never in the low bands. It is the plug-in hybrid, which existed in the gap between them, that has lost most of its tax advantage.
The plug-in hybrids that still make sense are the ones with genuinely long electric range used by drivers who genuinely plug in nightly, because those cars were always the honest version of the idea. If you were leasing one purely for the band, the band has moved.
What to Ask Before You Sign
Four questions, and all of them should be answered in writing on the order paperwork rather than verbally.
| Ask | Why |
|---|---|
| The exact CO2 figure for this derivative | Figures vary by wheel size and trim, and the range quoted on a brochure page covers several versions |
| Whether the car has been re-homologated | A model mid-way through re-approval may be quoted on either figure depending on build date |
| The expected registration date | Your band is fixed by the figure recorded at registration, not at order |
| The electric range on the same datasheet | A long range with a high CO2 figure usually means the utility factor change, not a weak car |
If a supplier cannot answer the first of those, that is reason enough to pause. Ask us and we will get it confirmed by the funder against the specific derivative before anything is signed.
Plug-in Hybrids Worth a Look
The ranges where the electric side is strong enough to justify the car.
Read Next
The guides that cover the tax and the technology in more depth.
Not Sure Which Figure Applies to Your Quote?
Send us the derivative you are looking at and we will get the CO2 figure and the registration timing confirmed in writing before you commit.
Talk to LetsLeaseFrequently Asked Questions
Because the sum changed, not the car. Every plug-in hybrid's official figure blends its petrol consumption with its electric running, weighted by the utility factor, which is the share of miles the test assumes you cover on battery. Euro 6e-bis rewrote that weighting to be far less generous. The engine, battery and electric range are untouched.
It is the test's estimate of how much of a plug-in hybrid's driving is done on electric power. A high utility factor pulls the blended CO2 figure down towards zero. The original version assumed drivers plug in more often than they actually do, and the Department for Transport's own estimate is that real-world CO2 from plug-in hybrids runs 243% above the WLTP figure.
The DfT's own worked examples show a car at 10 g/km with 80km of electric range moving to 30 g/km, one at 10 g/km with 120km moving to 40, one at 30 g/km with 40km moving to 60, and one at 30 g/km with 80km moving to 90. The lower the starting figure, the bigger the multiple.
Not as the minimum standard. Great Britain still runs Euro 6d, and adoption of Euro 6e-bis here has been the subject of government consultation rather than settled law. HM Treasury has said any change would apply to vehicles registered from 1 January 2026, subject to that consultation. Dates circulating on various websites, including an April 2026 start with a transition to 2028, are not ones we have been able to verify against published legislation, so we are not repeating them as fact.
HM Treasury has said there will be no retrospective changes to CO2 emissions values for vehicles already registered. Your figure is the one recorded against your car at registration. If you are mid-lease on a plug-in hybrid, nothing about this changes your current arrangement.
Barely. You are not paying benefit-in-kind, so the headline effect does not reach you. A car in the 50 to 75 g/km range attracts a higher first-year vehicle excise duty rate than one under 50, but it is a one-off and is usually built into the rental. Your actual running costs depend on how often you charge, which no test method changes.
Yes, significantly. The bands below 50 g/km are very low, and a plug-in hybrid that slipped under that line cost its driver a fraction of what an equivalent petrol SUV did. Crossing 50 g/km moves the car into a materially higher band, and because the charge is a percentage of list price the effect on an expensive SUV is not marginal. Bands and rates change each tax year, so check your own position with your accountant rather than relying on figures from a year ago.
It can be, but the case is narrower than it was. The plug-in hybrids that still stack up are the ones with genuinely long electric range driven by people who plug in nightly, because those were always the honest version of the idea. If you were choosing one purely for the tax band, the band has moved and a fully electric car is unaffected by any of this.
All of them, in principle, as they are re-homologated. BMW's own UK technical data for the X3 30e xDrive now lists 64 to 68 g/km against a 19.7kWh battery and 52 to 54 miles of electric range, which is a car with more than fifty miles of electric capability quoting a figure well above 50 g/km. Models work through re-approval at different times, so two cars on the same forecourt can be quoted on different test methods.
Ask for the exact CO2 figure for the specific derivative in writing, confirm whether that model has been re-homologated, and get the expected registration date, because your band is fixed by the figure recorded at registration rather than at order. Brochure ranges cover several wheel and trim combinations, so a range is not an answer. If a supplier cannot give you the derivative figure, that is reason enough to pause.
A second revision of the utility factor has been reported as tightening figures again, which would affect cars type-approved after it takes effect. We will not put a date on it here, because the ones in circulation are not ones we can verify. If your order straddles a possible changeover, ask us to get the figure confirmed by the funder before anything is signed.
LetsLease is a credit broker rather than the lender. We arrange the agreement and place it with a funder such as Lex Autolease, Novuna, Ayvens or Santander, and that funder owns the vehicle and holds the agreement with you. Because we work across several funders rather than one, we can compare how each prices the same car.