Should I buy a diesel car and what is their future?
Diesel cars have been given a hard time in recent years, but can still make a lot of sense for some drivers
A few years ago, a diesel car was the default option for a lot of drivers. Fuel-efficient, powerful and refined, cars fuelled from the black pump were massively popular and often held their value better than petrol models.
But that all changed, as despite their ability to consume less fuel than equivalent petrol engines and generally emit less CO2, the higher cost of diesel fuel and revelations surrounding their other harmful emissions led to a sudden and dramatic fall from grace.
Diesels also used to enjoy lower Vehicle Excise Duty (commonly known as road tax) than petrols, but they’ve been pushed out of fashion, with sales shrinking, by a succession of tax increases, parking surcharges and city centre low-emission zones that penalise older diesels.
Another factor that might put off some buyers was the announcement that sales of brand-new petrol and diesel cars woukd be banned in 2030, although this has now been put back to 2035.
The demise began in 2015 and the emergence of the ‘Dieselgate’ scandal, accelerated by the introduction of strict government measures designed to limit the amount of exhaust emissions – specifically Nitrous Oxide – polluting the air in the UK's city centres.
All of which sounds like miserable news, but diesel cars can still be very much the best option for some drivers – especially those who do lots of long journeys. Read on to find out if you should buy a diesel car.
Diesel cars in London
London's Ultra-low Emission Zone (ULEZ) first began operating in April 2019 and imposes a compulsory charge of £12.50 for the majority of pre-2015 diesel vehicles entering the city with a view to deterring their use and reducing air pollution. The area affected grew dramatically in October 2021 and again in August 2023, so this now applies to the vast majority of London and many of its suburbs.
The capital’s ULEZ scheme has been followed by a succession of new clean air zones (CAZ) being set up in city centres around the country, which will also mainly target diesel cars, as these can produce high levels of certain exhaust emissions.
With this in mind, you'd be forgiven for steering clear of diesel altogether when you choose your next car. Many drivers are doing just that and new diesel car sales have fallen dramatically over the past few years.
To counter this latest hurdle, the latest diesel cars have been developed to produce fewer emissions and meet the ‘Euro 6’ emissions standard that the ULEZ and other clean air zones require, so the risk of being caught out by additional fees for driving a diesel car have been notably reduced for now. Virtually every brand new car sold since September 2015 has had to comply with the Euro 6 limits.
Diesel cars still remain cheaper to run than petrol cars for most high-mileage drivers thanks to excellent fuel economy, and their efficiency is still remarkably impressive.
Diesel engines also have a lot more low-down torque and their pulling power is ideal for towing, as well as for larger vehicles such as SUVs and pick-ups. Modern diesels meeting Euro 6 emission limits are exempt from ULEZ, CAZ and low emission zone charges, so if you are in the market for a bigger vehicle, a diesel engine is often still the best way to go.
And while some believe the Doomsday clock is counting down with petrol and diesel new cars to be withdrawn from sale by 2035, they will still be allowed on the road and there are no immediate plans to withdraw fossil fuels of any kind from the forecourts.
As a general rule, here is when you should choose a diesel over a petrol or alternatively fuelled car:
Consider a diesel for...
✔ High annual mileages
✔ Big vehicles, including SUVs
✔ Larger company cars
✔ Towing heavy loads
Choose petrol for...
✔ Driving less than 12,000 miles per year
✔ Small- or medium-size vehicles
✔ Mainly city driving (especially London)
✔ Lower air pollution impact
Not all diesel cars are subject to emissions surcharges and you can reduce the risk of being hit with inner-city emission charges by buying a newer diesel car that complies with the latest emissions regulations, called Euro 6.
These vehicles are not subject to charges in London’s ultra-low emission zone (ULEZ), nor the clean-air zone which has been in place in Birmingham since 1 June 2021, nor are they charged in similar schemes across urban areas in the UK.
Every car registered since September 2015 is required to meet the Euro 6 standard, although there are several examples of diesel cars that met this standard prior to it becoming a requirement. All diesel Mazda CX-5 models have met the standard since 2012 for example, so they should be exempt from inner-city charges.
Cars that meet future emissions regulations (called RDE2 or Real Driving Emissions Step 2, or Euro 6d) are exempt from recent road tax increases. These include some versions of the Mercedes A-Class, the the BMW 2 Series Active Tourer and BMW 2 Series Gran Tourer, the Ford Kuga and the Volkswagen Golf – all popular models.
All brand-new cars comply with the latest Euro 6 regulations and there are no plans to charge owners of these vehicles for driving in city centres in the next few years, so in many ways a new diesel can still make a lot of sense.
Those that only meet the previous, Euro 4 or 5 emissions standard are subject to emissions charges in London and some other cities and will only make sense if you don’t really do much urban driving.
When you’re buying a used car, you should check which standard it meets – it’ll be written on the V5C registration document so you will be able to see it with the car’s paperwork.
Like many retailers, BuyaCar publishes the Euro standard of each used car in the technical information that accompanies its listings. It’s worth asking for this to be double-checked when you come to make a purchase to ensure that your car is compliant if this is something that is important to you.
Diesel car values started to fall steeply about five years ago and today they hold their value less than petrol cars.
But as long as diesel cars become cheaper, they offer very good value for money, even with extra taxes and charges, which is likely to lure some buyers back. Larger vehicles hold their value better in diesel form, as petrol versions can be extremely expensive to run, and the buyers’ need is often different. Those who tow for example, or need a utility vehicle for work, keep demand much higher for such vehicles than for a diesel compact hatchback.
To protect yourself against the uncertainty of depreciation, taking out PCP finance will mean you don’t have to shoulder the risk of the car falling heavily in value, should demand for diesels reduce.
This is because PCP finance gives you the choice of keeping your car at the end of the contract by paying a pre-agreed lump sum, or handing it back with nothing more to pay even if it has lost much more value than initially expected, assuming you keep it in good condition and don’t exceed the mileage cap.
After initially announcing that the sale of new petrol and diesel cars will be banned by 2030, the government has controversially changed the date to 2035.
But there are no plans to ban petrol or diesel cars from the roads entirely, so second-hand sales are expected to be unaffected. However, London's mayor has proposed banning them from driving in the capital, starting with the centre in 2025. Other cities may follow suit.
Should I buy a diesel as a low-mileage driver?
The simple answer here is no. If you drive fewer than 12,000 miles per year, then a petrol car is likely to be a better option, particularly if you’re looking for a small or medium model.
Petrol vehicles generally have a lower price than diesel cars, and require less specialist maintenance. For example, diesels that don’t get driven long distances tend to suffer from blocked diesel particulate filters, which are used to reduce the nitrous oxide emissions to start with.
Typically you need to drive more than 12,000 miles per year for the lower fuel costs of a diesel car to outweigh the higher purchase price.
It’s also worth considering an electric car. Most EVs including the Volkswagen ID.3, Peugeot e-208 and Jaguar I-Pace, plus cheaper models from the likes of MG, Hyundai and Kia, can all achieve upwards of 200 miles on a single charge
Advancements in engine technology have brought petrol engines closer to the fuel economy figures of diesel motors, particularly in smaller and lighter cars.
That means that any fuel savings you'll make by choosing a diesel supermini or family car are likely to be small, and may not make up for the higher purchase price that diesel cars typically have.
Before you make your decision, it is worth checking the real-world fuel economy of a new car. Some of the most advanced petrol and diesel engines are extremely good at returning high mpg figures during the official European fuel economy test, carried out in a laboratory, but deliver much lower figures in normal driving.
Recent announcements of clean air zones have confirmed that diesel car drivers will face hefty charges or outright bans in some city centres, including London, Birmingham and Glasgow. It makes the choice of petrol a no-brainer for drivers who rarely stray out of town - particularly if you’re looking for a cheap car that’s a few years old or more, which is unlikely to meet the latest emissions regulations.
Newer diesels, which meet the Euro 6 standard, should initially be exempt from clean air zone charges because they are less polluting, but they still don't make the best city cars.
Petrol or electric vehicles have always been best for short journeys, such as shopping trips or the school run because they don’t need exhaust filters. Modern diesel cars have these filters to trap harmful soot particles, which can become clogged unless you regularly make long journeys on faster roads, when hotter exhaust gases are able to burn off the particles are produced.
City drivers will also benefit the most from hybrid cars, which can recover energy that’s normally wasted during stop-start driving. In these situations, fuel economy is considerably better than in conventional petrol vehicles.
Microscopic soot fragments from car exhausts - known as particulates - and nitrogen oxides are known to contribute to respiratory diseases and are responsible for tens of thousands of early deaths in Britain each year. Diesel cars emit far more of these pollutants than petrol vehicles.
Euro 6 emissions regulations were meant to bring diesel emissions in line with petrol cars, but real-world testing suggests that many cars don’t come close to the required standard when they are driven on the road.
These vehicles still remain legal because they pass the official emissions test, which is carried out in a laboratory, but if the pollution produced by your car is a big concern - particularly if you drive in built-up areas, where it's most likely to affect people - then until recently, a non-diesel car has been best.
This is likely to change in coming years, as new cars will have to pass a much tougher test, carried out on public roads, known as Euro 6d. An interim test, which isn't quite as tough, has been introduced to give car makers time to re-engineer their cars and it is already having an effect. Research from Germany suggests that many of the very latest diesel cars almost match petrol versions for harmful nitrogen oxide emissions - and a few are cleaner.
Where diesel still really makes sense is for long-distance or business drivers. If you travel more than 15,000 miles a year, then the additional cost of a diesel car should be outweighed by the savings you make from its better fuel economy. The larger the car, the more likely this is to be the case.
The air pollution impact of diesel cars is also less when they are driven outside of built-up areas, as the harmful emissions can disperse with far less impact on health.
Buy a newer diesel car that meets the Euro 6 emissions regulations and you shouldn’t even be penalised for entering cities.
As a rule, diesel engines are more efficient than petrol models. In heavy cars, which need more energy to get moving, that difference adds up to greater savings. But you need to work petrol cars much harder to get that same surge of power, reducing fuel economy. It’s not uncommon for an SUV with a diesel engine to offer twice the fuel economy of the petrol equivalent, and that’s where the balance really shifts.
That’s why diesel is still the fuel of choice for people carriers, SUVs and pick-ups, where you should choose a diesel car for reasons of both efficiency and cost.
Furthermore, the current company car tax regime is still linked to CO2, so you may make savings with a diesel vehicle. Diesel cars are 4% higher to tax than petrol vehicles, though, which makes small petrol cars cheaper for lower mileage business users.
Diesel engines are more efficient than petrol models. In heavy cars, which need more energy to get moving, that difference adds up to greater savings.
The way that diesel engines work also makes them more suited to larger cars: you don't need to press the accelerator hard or work the engine quite as much to feel a burst of power. Even a medium-size diesel engine is powerful enough to get a big and heavy SUV moving quickly, with little apparent effort.
In contrast, you need to work many petrol cars hard to get that same surge of power, reducing fuel economy even further. It’s not uncommon for an SUV with a diesel engine to offer around twice the fuel economy of the petrol version of the same vehicle.
That makes diesel the fuel of choice for people carriers, SUVs and pick-up trucks. Some hybrid SUVs combine a petrol engine with an electric motor, which offers impressive fuel economy on shorter journeys, but they aren't ideal for everyone because their efficiency quickly drops on longer trips, and the cars are far more expensive to buy than their petrol or diesel counterparts.
The new car tax system has reduced much of the advantage that diesel vehicles used to have because, unlike the previous system, it’s no longer solely based on carbon dioxide emissions (CO2). This reduces the incentive for drivers to buy diesel-powered cars.
However, the current company car tax regime is still linked to CO2, so you may make savings with a diesel vehicle.
It will have to be efficient, though, because rates for diesel cars are 4% higher than petrol vehicles. This makes small petrol cars cheaper for business users. But large diesel-powered cars, including SUVs, are so much more fuel-efficient than petrol versions, that they tend to attract cheaper rates of company car tax.
As business users tend to run brand new cars, vehicles should comply with the current Euro 6 emissions regulations, so won't be affected by the London clean air zone.
Just as diesels are best at getting heavy vehicles moving, they are also the engine of choice for towing. Their substantial low-engine-speed pulling power - known as torque - is much more effective at hauling a heavy caravan or trailer away from a standstill or up a hill.
In smaller cars, petrol engines may simply not be up to the job and not be able to cope with towing loads up steep hills. Even if they can pull away, the fuel bills may give you nightmares compared with a diesel alternative.
In all cases, the golden rule is to think carefully about what you will use a car for before choosing which one to buy – as you can see above there are many reasons why, even today, you should buy a diesel car and there’s a vast selection of modern, efficient diesel cars to choose from on BuyaCar.