Wind the clock back ten years and diesel cars made up around 50% of the UK’s new car market, according to figures from the SMMT. In 2025, that’s dropped to just 5.8% - a massive decline.
But around 11 million diesel cars still operating on UK roads, it’s not as if the fuel is going away any time soon.
So, should you buy a diesel? If you’re looking to buy a used diesel, which should you buy? And how do you avoid Clean Air Zone or ULEZ fines by buying the right one? We reveal all in our one-stop diesel car guide.
Are diesel cars bad?
So, why did diesel cars go from being considered a ‘greener’ motoring choice than petrol to being labelled ‘dirty’ and harmful to the environment?
Well, it all comes down to the emissions from a diesel car’s exhaust pipe. Or, more specifically, the exhaust pipes of older diesel vehicles.
While diesel engines generally emit lower levels of carbon dioxide (CO2) than an equivalent petrol engine, they also emit considerably higher levels of nitrogen oxides (NOx) and particulate matter.
NOx emissions are closely linked to respiratory problems including asthma and, with long-term exposure, chronic lung disease. They’re also a major component of ‘smog’ – intense clouds of air pollution. In high concentrations they can even help form acid rain, damaging ecosystems.
Particulate emissions are equally nasty. Fine particles like PM2.5 (emitted by diesel exhausts) can penetrate deep into the lungs and bloodstream, causing several serious health problems including respiratory and cardiovascular problems. They’re also carcinogenic, increasing the risk of things like lung cancer.
Diesel emissions and concerns over public health are nothing new. In fact, scientists first began studying how vehicle emissions affect air quality back in the 1940s.
However, during the UK and Europe’s diesel boom of the 2000s, such concerns took a back seat to the belief that diesel’s reduction in CO2 emissions over an equivalent petrol car outweighed any air quality concerns.
Are diesel cars being banned or phased out?
The UK Government intends to ban the sale of new petrol and diesel cars either by 2030 or 2035, depending on the results of an industry consultation. Vans, too, will need to be 100% zero emission by 2035.
So yes, new diesel vehicles will eventually be banned from sale. But, as thing stand, there are no plans to ban existing diesels from the road, nor outlaw the sale of used diesel cars.
With millions of diesel cars and vans in use on UK roads, it’s unlikely we’ll see any sort of overall ban put into place for many years. Isolated cases, such as Bristol Council considering a full-on ban of diesels back in 2019, haven’t come to fruition.
However, diesels are currently being phased out by many car companies, with considerably less choice of diesel cars (particularly smaller ones) in new car ranges.
Larger new diesel cars are still fairly common but expect them to be gradually moved over to hybrid or electric options in time.
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Diesel cars and London ULEZ
London’s Ultra Low Emission Zone, or ULEZ, is a scheme designed to reduce the level of harmful emissions in the UK capital’s air by discouraging drivers of older, more polluting vehicles from driving into it.
Originally only affecting an area of Central London, the ULEZ zone expanded to cover all London boroughs in 2021. Drivers of the most polluting cars, motorcycles and vans must pay a £12.50 daily charge to enter the city.
The ULEZ zone affects owners of both petrol and diesel cars. However, the rules on diesels are much stricter. Petrol cars need to meet Euro 4 emissions standards to avoid paying for ULEZ (that’s generally those registered after 2006) while diesel cars need to meet Euro 6 (cars registered after September 2015, and some prior to that date).
In essence, you’ll need to buy a much newer diesel car than if you owned a petrol car to avoid the fines.
Data from the London Assembly claims that NOx emissions from cars are estimated to be 13 per cent lower than they would’ve been without the expanded ULEZ zone, while particulate emissions (PM2.5) are down 22 per cent.
While the Euro 6 standard required for diesels to meet ULEZ compliance is the latest emissions standard, motorists are concerned that the ULEZ scheme will adopt stricter standards when Euro 7 comes into force in late 2026.
A response to a Freedom of Information Request (FOI) made to Transport for London (TfL) in December 2023 claimed that there are “no plans to change the ULEZ standards at present”.
“The current standards help the Mayor and TfL strike the right balance in maximising the benefits to Londoners by encouraging people to use less polluting vehicles while also ensuring compliant vehicles are no unaffordable to people who rely on private vehicles to make a journey”.
The response also outlines that a formal public consultation will need to take place before any changes to the existing scheme could be made.
Diesel cars and other Clean Air Zones
There are plenty of cities utilising Clean Air Zones aside from London. As of March 2025, there are Clean Air Zones operating in 14 cities across the UK.
Many of these zones are actually targeting buses, coaches, taxis and HGVs or vans instead of private cars. But Aberdeen, Birmingham, Bristol, Dundee, Edinburgh and Glasgow all charge car drivers either a daily fee or (in Scotland) a more expensive penalty charge if their vehicle is not compliant.
All of these clean air zones mirror the standard used by London’s ULEZ zone: for diesel cars, that means they must meet the latest Euro 6 emissions regulations.
Is diesel tax higher?
The days of diesel cars getting favourable tax rates are long over, but you won’t actually pay more in car tax (otherwise known as Vehicle Excise Duty, or VED) for a diesel car over an equivalent petrol.
In the current car tax system, the bands (and therefore the tax rates) are determined by a car’s CO2 emissions and any electric range the car has if it’s a plug-in hybrid or EV. This is actually favourable to diesels, which typically produce less CO2 in driving.
There will be some changes to car tax in April 2025, but diesels aren’t affected for the most part – only the lowest emitting diesels registered between 2001-2017 that previously paid zero tax will now be moved from Band A to Band B, bringing the charge up to £20 a year.
For new cars, the first-year rate is based on CO2 emissions, but all non-electric vehicles pay a £190 a year flat rate for every year after that. That applies to post-2017 cars if you’re buying used.
The main area that has changed for diesel car drivers in recent years is company car tax, or Benefit-in-Kind tax. Previously diesels were incentivized with favourable tax rates, but that changed in 2018 as concerns grew over diesel emissions.
Then, diesels that didn’t pass the latest real-world driving emissions tests (known as RDE2) faced a 4% surcharge over an equivalent petrol car. Meanwhile, plug-in hybrid and electric models became greatly incentivised.
As of April 1st 2025, if you choose a new 2.0 TDI diesel Volkswagen Golf as you company car you’ll fall into the 30% company car tax band, paying over £2,000 a year as a 20% taxpayer and over £4,000 a year as a 40% taxpayer.
That’s slightly higher than the equivalent 1.5 TSI petrol model. Meanwhile, if you’d gone for a Volkswagen ID.3 electric car a 20% taxpayer would pay just £225 a year, and a 40% taxpayer would pay £450 a year
Should I buy a new diesel car?
New diesel cars have sophisticated emissions reduction systems that have helped greatly reduce harmful pollutants, such as NOx and particulate matter. However, you should still think carefully about whether a new diesel car is right for you.
Firstly, there’s the lack of choice of new diesel cars. Many car companies are either gradually phasing out diesels from their range, or have already removed them entirely. Large brands such as Vauxhall, Toyota, Hyundai, Nissan, Honda, Dacia, MINI and Volvo no longer offer any diesel models.
However, there are still brands such as Volkswagen, BMW, Mercedes-Benz, Audi and Land Rover that offer several new diesel cars in their lineup.
Secondly, it’s worth thinking about the complexity of the latest diesel engines. The emissions reduction systems used are incredibly clever, but need maintaining.
For example, most diesel engines now use AdBlue, a fluid partially made up of urea that is injection into the exhaust system to convert NOx emissions into harmless nitrogen and water.
On average, a full tank of AdBlue lasts between 5,000 and 8,000 miles depending on the car. When it’s empty, you’ll need to source AdBlue from a fuel station or elsewhere and add it to the car’s tank along with diesel. This is considered an inconvenience by many.
The AdBlue system also introduces numerous sensors, injectors and pumps that can fail over time and use, potentially adding to long-term reliability concerns.
A similar problem is diesel particulate filters (DPFs). These capture particulate matter from diesel exhausts, but can fill up over time, needing ‘regeneration’ to burn them off.
If a diesel car is used for short journeys and only in town, it might not reach proper operating temperature, which can lead to improper regeneration and soot build up. A clogged DPF can reduce performance, increase fuel consumption and potentially damage your car – and new DPFs can be very expensive.
For that reason, we recommend thinking about your annual mileage and types of journeys before buying a new diesel car – typically, above 12,000 miles a year is the cut-off point where diesels make more financial sense.
If you’re typically driving around town or short distances where the engine doesn’t get up to operating temperature, then a petrol, hybrid or electric car is probably a better bet.
Should I buy a used diesel car?
If you’re shopping for a used diesel car, it’s worth thinking about what age of car you can afford. Generally speaking, the newer the diesel car is the less polluting it is.
All diesel cars registered after September 2015 in the UK meet the Euro 6 emissions standard, meaning they are not subject to ULEZ or Clean Air Zone charges or penalties.
Some diesel cars met this standard before 2015 – you can check if it does via the car’s V5C logbook or using the Government’s Clean Air Zone checker.
If you’re looking at buying an older diesel car that doesn’t meet Euro 6, you’ll need to think about how often you plan on entering large towns and cities in it.
While only a handful of cities in the UK have chargeable Clean Air Zones in place, more are expected to join in time. Expect pressure on local authorities to reduce local air pollution to only increase.
So, although popping to your local town for some shopping in an older diesel may be fine now, it may not be in a couple of years’ time. The upside is that these older diesels can often be cheaper to buy because of these Clean Air Zone restrictions.
So, if you live in a more rural area, and don’t intend on driving you car into a built-up area, it could be an excellent way into an affordable and fuel-efficient used car. Don’t write off diesel just yet.
Diesel car FAQs
Is it wise to buy a diesel car now?
It depends on your situation. Diesel cars only make more sense than petrols if you are doing higher than average mileage – around 12,000 miles. Older diesels are more polluting than newer ones, too, and are subject to penalty charges or fines if they enter certain cities.
Can I still drive my diesel car after 2030?
Absolutely. While the sale of new diesel cars will be banned in that year, there are no plans to ban existing diesels from the roads – just charges and penalties if you try to enter some cities in an older, more polluting diesel.
What is classed as a short journey in a diesel?
Put simply, a short journey in a diesel is one where the car’s engine doesn’t reach its proper operating temperature – typically around 90ºC. It varies depending on the car, but many diesels can take five miles or more to reach their operating temperature.
