Introduction
Diesel has fallen out of fashion. For drivers who cover high mileage it still makes financial sense. A modern diesel can return well over 60mpg on official figures, which few petrol cars can match outside the hybrid class.
Here are ten of the most fuel efficient diesel cars to buy in the UK, with official and real-world mpg, strengths and weaknesses for each and a look at why diesel has changed so much.
Summary:
- Best for small-car economy: The Peugeot 208 1.5 BlueHDi returns 71.4mpg on official figures.
- Best real-world economy: The Skoda Octavia 2.0 TDI is the most economical diesel What Car? has tested, at 57.9mpg.
- Best premium choices: The Audi A4 35 TDI and Mercedes C220d both pass 60mpg officially.
- Expect 10% to 13% less in real life: The What Car? tests put the Octavia at 57.9mpg and the A4 at 52.2mpg.
- Diesel suits high mileage: Carwow says it generally makes sense above roughly 12,000 miles a year.
- Choose Euro 6: Diesels meeting Euro 6 are compliant with London's ULEZ.
Why Were Diesel Cars So Popular?
Diesel's rise was driven by economy and tax. Diesels use less fuel than petrol equivalents, which also means lower CO2 emissions. Diesel cars benefited when the UK introduced a CO2-based annual ownership tax in 2001.
An Open University review found that CO2-based company car tax from April 2002 favoured diesel and led to a substantial rise in sales. Better technology helped too. Common rail injection and turbochargers gave diesels more torque, smoother running and quieter performance. UK diesel sales more than doubled to over 300,000 between 1995 and 2000, according to Just Auto.
Why Are Diesel Cars Better Now?
Today's diesels are far cleaner than those of the early 2000s. Euro 6 caps diesel car nitrogen oxide (NOx) emissions at 80mg/km, against 180mg/km under Euro 5, which Fleet News says more than halves the figure.
Manufacturers meet the limit with technology such as selective catalytic reduction, which injects AdBlue into the exhaust. Bosch claims its system can cut NOx by up to 95%. Diesel particulate filters trap soot, with What Car? saying they can cut particulate emissions by up to 90%.
The result is that Euro 6 diesels can enter London's ULEZ without charge, while still delivering the economy that made diesel popular.
Is a Diesel Right for You?
Diesel engines are efficient on longer journeys and at motorway speeds. Short, cold trips suit them less, because diesel engines only fully warm up after a few miles.
Carwow suggests diesel generally suits drivers covering more than 12,000 miles a year, since the savings at the pump then outweigh the extra costs of buying and maintaining one. Diesel fuel is also now priced above petrol, which narrows the gap.
Buying the Most Economical Diesel Cars
The list is a tempting one. Each diesel below is built to keep running costs low, with strengths, weaknesses and the mpg figures that matter.
| Model | Engine | Official mpg | Real-world mpg (What Car?) |
|---|---|---|---|
| Peugeot 208 | 1.5 BlueHDi | 71.4mpg | Not tested |
| Vauxhall Corsa | 1.5 Turbo D | 70.6mpg | Not tested |
| Skoda Octavia | 2.0 TDI | 64.2mpg | 57.9mpg |
| Volkswagen Golf |
2.0 TDI | 63.5 to 64mpg |
Not tested |
| Mercedes C-Class |
C220d | 62.8mpg | Not tested |
| Audi A4 | 35 TDI | 60.1mpg | 52.2mpg |
| Skoda Superb | 2.0 TDI | 57.6mpg | 54.8mpg (Estate) |
| SEAT Leon | 1.6 TDI | 57.6mpg | 56.0mpg (Ecomotive, 2013 to 2020) |
| Ford Mondeo | 1.5 diesel | Not stated | 53.7mpg |
| Renault Kadjar | 113bhp diesel | Not stated | 55.2mpg |
Official figures come from Cinch and Auto Express and apply to specific versions. Real-world figures come from What Car?'s Real MPG tests, updated in February 2024. Versions may not match exactly.
1. Peugeot 208 1.5 BlueHDi
Launched in 2019, the Peugeot 208 is a five-door supermini with sharp styling and a 1.5-litre BlueHDi diesel that officially returns 71.4mpg. The figure makes it the most economical car on this list on paper and a strong choice for high-mileage drivers who want a compact car.
Inside, the dashboard is stylish and unusual, with instruments placed so they're read over the steering wheel rather than through it. The layout feels distinctive, although it takes a little getting used to.
Strengths
- Best official economy of any car here
- Compact supermini that suits town and motorway
- Stylish, distinctive interior
Weaknesses
- The instrument position doesn't suit every driver
- Supermini space is limited for families
- Real-world mpg hasn't been independently tested by What Car?
Official mpg: 71.4mpg
2. Vauxhall Corsa 1.5 Turbo D
The Vauxhall Corsa shares its 1.5-litre turbo diesel with the Peugeot 208 and claims 70.6mpg on official figures. The 2019 model is a straightforward, easy-to-live-with supermini that keeps fuel bills low without any complicated technology to learn.
Cinch notes that the Corsa's design is shared with the Peugeot. The two cars are natural rivals. Buyers can compare them back to back and choose on styling, price and condition.
Strengths
- Official economy of 70.6mpg
- Same efficient engine as the 208
- Simple, practical supermini
Weaknesses
- Styling is a matter of taste
- Limited rear space compared with larger hatchbacks
- Real-world mpg hasn't been independently tested by What Car?
Official mpg: 70.6mpg
3. Skoda Octavia 2.0 TDI
The Skoda Octavia is the most economical diesel What Car? has tested, returning 57.9mpg in its Real MPG test against an official claim of 64.2mpg. Frugality comes with a huge boot and a spacious cabin, especially in Estate form.
Auto Express praises its comfortable ride and smart interior and says it should be near the top of any shopping list. Cinch adds that it's cheap to buy and run, with a 0 to 62mph time of 8.5 seconds.
Strengths
- Best real-world economy of any diesel What Car? has tested
- Huge boot and roomy interior
- Comfortable ride
Weaknesses
- Rear headroom is a little tight
- Rivals can be more fun to drive
Official mpg: 64.2mpg
4. Volkswagen Golf 2.0 TDI
The Mk8 Volkswagen Golf claims about 64mpg with the 150hp 2.0 TDI and 63.5mpg with the 114bhp version. Digital instruments and smartphone connectivity bring the cabin up to date. The car feels well built on the road.
Auto Express calls it one of the best Golf generations yet, with reassuring ride and handling and a diverse engine range. The Golf is a sensible all-rounder for drivers who want a compact family hatchback with strong economy.
Strengths
- Around 64mpg on official figures
- Modern tech including digital instruments and Apple CarPlay and Android Auto
- Reassuring ride and handling
Weaknesses
- Less roomy than the Octavia
- Cabin quality has drawn some criticism
- Road noise on larger wheels
Official mpg: 63.5 to 64mpg
5. Mercedes C220d
The Mercedes C220d claims 62.8mpg, which is impressive for a premium saloon. Auto Express praises its on-board technology and cabin quality. The range also includes a plug-in hybrid option for buyers who want to compare.
Drivers who want comfort and a quality interior without giving up economy are well served here. Running costs can climb though. Check service history and the cost of parts before buying.
Strengths
- 62.8mpg is strong for a premium saloon
- High-quality cabin
- Improved on-board technology
Weaknesses
- Can be expensive to run
- Larger wheels affect ride comfort
- Smaller boot than some rivals
Official mpg: 62.8mpg
6. Audi A4 35 TDI
The Audi A4 35 TDI claims 60.1mpg and reaches 62mph in 8.2 seconds, which pairs brisk performance with premium economy. What Car? recorded 52.2mpg in its Real MPG test, still enough to rank among the most economical diesels it has tested.
The cabin is among the best built in its class, smooth and packed with technology. Some rivals are more fun to drive. Few feel as polished at motorway speeds.
Strengths
- Premium interior with plenty of technology
- Brisk performance for an economical diesel
- Smooth and refined
Weaknesses
- Real-world economy is around 13% below the official claim
- Some rivals are more fun to drive
- Used prices vary widely by age and specification
Official mpg: 60.1mpg
7. Skoda Superb 2.0 TDI
The Skoda Superb offers a cavernous interior and boot, with 57.6mpg officially from the 148bhp diesel. The more powerful 190bhp version drops to about 47.9mpg, which makes the lower-powered engine the one to choose for economy.
What Car? tested the 2.0-litre diesel Estate at 54.8mpg in real conditions, which is strong for such a big car. Auto Express highlights the upmarket design and the generous equipment.
Strengths
- Huge interior and boot
- Strong real-world economy for its size
- Upmarket design and plenty of features
Weaknesses
- Not exciting to drive
- The 190bhp version is far less economical
- Not as cheap as it used to be
Official mpg: 57.6mpg
8. SEAT Leon 1.6 TDI
The SEAT Leon 1.6 TDI claims 57.6mpg and is a good-value way into diesel ownership. Insurance costs are low and the 380-litre boot expands to 1,470 litres with the seats folded.
What Car? tested the 2013 to 2020 Leon Ecomotive at 56.0mpg in real conditions, a strong result for a hatchback of this size. The Leon is also better to drive than some rivals, although road noise is more noticeable.
Strengths
- Low insurance costs
- Large, flexible boot
- Strong real-world economy
Weaknesses
- An older model where condition and history matter
- More road noise than some rivals
- Real-world figure is for the Ecomotive version
Official mpg: 57.6mpg
9. Ford Mondeo 1.5 Diesel
The Ford Mondeo was built from 2014 to 2022 and is now only available used. What Car? found the 1.5-litre diesel the most economical engine in the range, returning 53.7mpg in its real-world test.
The Mondeo is a spacious, comfortable executive car with a reputation for reliability, which makes used examples attractive for drivers covering long distances. Plenty of space for the money is the main appeal.
Strengths
- Strong real-world economy for a large car
- Spacious and comfortable
- Reliable executive car, according to What Car?
Weaknesses
- No longer built, which leaves only used examples
- Older design and technology than newer rivals
- The economy engine is the smaller 1.5 rather than the 2.0 TDCi
Real MPG Average: 53.7mpg
10. Renault Kadjar Diesel
The Renault Kadjar is the most frugal family SUV What Car? has tested, returning 55.2mpg with its 113bhp diesel. A larger boot than the Nissan Qashqai makes it a practical choice for families.
For buyers who want a higher driving position without a big fuel bill, a used Kadjar is a sensible option. Check the service history carefully, since diesels in SUVs are often used for short family trips.
Strengths
- Most economical family SUV What Car? has tested
- Larger boot than the Nissan Qashqai
- Higher driving position than a hatchback
Weaknesses
- Modest 113bhp output
- Short family trips can be hard on a diesel particulate filter
Real MPG Average 55.2mpg | Town 50.0mpg | Motorway 48.8mpg | Rural 69.1mpg
Official vs Real-World Fuel Economy
Official figures are a useful guide but rarely what drivers see. What Car? runs its Real MPG tests on a rolling road under controlled conditions, with tailpipe emissions sampled every second.
The 2.0 TDI Octavia returned 57.9mpg there against a 64.2mpg claim, roughly 10% lower. The Audi A4 35 TDI managed 52.2mpg against 60.1mpg, around 13% lower.
Real-world economy is still strong. The Octavia came out as the most economical diesel What Car? has tested. The A4 also makes its top ten.
Diesel and ULEZ: What to Know
Euro 6 diesels can enter London's ULEZ and other clean air zones without charge. Older Euro 4 and Euro 5 diesels pay £12.50 a day in London, according to Carwow.
Euro 6 was introduced from September 2015, although some cars sold up to 2016 may still be Euro 5. Check the registration on TfL's vehicle checker before buying.
Buying a Used Diesel: What to Check
- Service history: A full record matters more on a diesel than on a petrol.
- Driving pattern: Mostly short trips can clog particulate filters. Ask how the car was used.
- Warning lights: Check the dashboard for engine or emissions warnings on the test drive.
- Emissions standard: Confirm it meets Euro 6.
- History check: Run a full used car history check before paying.
Still deciding on fuel type? Compare options in our petrol vs diesel vs hybrid guide.
Conclusion
Diesel is no longer the default choice. For high-mileage drivers it still delivers the best economy outside hybrids and electric cars. The 208, Octavia and Golf stand out for value, while the C220d and A4 add a premium feel.
Match the car to the way it will be driven. Longer journeys suit diesel while short trips do not.
Frequently Asked Questions
What is the most fuel-efficient diesel car?
Among the cars here the Peugeot 208 1.5 BlueHDi leads on official figures with 71.4mpg. The Skoda Octavia 2.0 TDI leads on real-world economy, with 57.9mpg in What Car?'s tests.
Why were diesel cars so popular?
Better fuel economy and a tax system that rewarded low CO2 emissions drove demand. CO2-based ownership tax from 2001 and company car tax from 2002 both favoured diesel.
Why are diesel cars better now?
Euro 6 diesels emit far less nitrogen oxide than older ones, thanks to technology such as AdBlue systems. Particulate filters also trap most soot.
Are diesel cars still worth buying?
For drivers covering more than about 12,000 miles a year, yes. Lower-mileage drivers and those making mostly short trips are usually better served by petrol or hybrid.
Are diesel cars ULEZ compliant?
Euro 6 diesels are compliant. Older Euro 4 and Euro 5 diesels usually pay the daily charge.
How much mpg should a good diesel car get?
Many modern diesel hatchbacks and saloons claim 55 to 70mpg on official figures. Real-world economy is usually lower.
