Comparing petrol and diesel for UK drivers

Why petrol and diesel still divide UK drivers

Walk onto any forecourt and you’ll see two fuels, two price boards, and a decision that still trips up plenty of sensible people. For years, diesel was the obvious choice for anyone covering big miles: better fuel economy, more torque, and lower CO2 emissions than equivalent petrols. Then came dieselgate, clean air zones, and a shift in tax rules. Meanwhile, petrol engines became smaller, turbocharged, and far more efficient. The result? There’s no single right answer. The best fuel for you depends on how you drive, where you drive, and how long you plan to keep the car.

How the two fuels actually differ

Petrol engines use a spark to ignite the fuel-air mixture. They tend to be smoother, quieter at low speeds, and cheaper to buy. Modern small-capacity turbo petrols can return 45–50mpg on a gentle run, and they produce fewer harmful particulates than diesels. Servicing is generally simpler, and there’s no diesel particulate filter (DPF) or AdBlue to worry about.

Diesel engines rely on compression ignition. They deliver strong low-down torque, which makes them relaxed on the motorway and excellent for towing. A modern diesel can easily achieve 55–65mpg on a steady cruise. But diesels produce more nitrogen oxides (NOx) and particulates, and they need regular longer runs to keep the DPF healthy. Short, stop-start journeys can clog that filter, leading to expensive repairs. Diesel also typically costs a few pence more per litre at the pump.

When petrol makes more sense

If your annual mileage is modest — say under 12,000 miles — and most of your journeys are short hops around town, petrol is usually the smarter financial choice. You’ll pay less upfront, fuel is cheaper per litre, and you avoid the DPF headaches that plague low-mileage diesel drivers. A petrol car is also simpler and cheaper to maintain, and it won’t be caught out by tightening urban restrictions on older diesels.

• You drive fewer than 12,000 miles a year.
• Your typical trip is under 20 minutes or mostly urban.
• You want lower purchase and servicing costs.
• You rarely carry heavy loads or tow.

When diesel still earns its keep

Diesel remains a brilliant choice for high-mileage drivers who spend long stretches on motorways. If you cover 15,000 miles or more annually, the superior fuel economy can outweigh the higher purchase price and servicing costs. The torque also makes light work of caravans, trailers, and fully loaded cars. The key is to give the engine regular longer runs so the DPF can regenerate properly. A diesel that only ever does the school run is a false economy.

• You cover 15,000+ miles a year, mostly on faster roads.
• You tow a caravan, trailer, or regularly carry heavy loads.
• You keep cars for many years and can recoup the upfront premium.
• You can commit to a weekly 20-minute motorway run.

The numbers that matter: running costs, tax, and depreciation

Do the maths before you sign. Compare real-world mpg, not brochure figures. As a rough guide, if petrol costs £1.45 per litre and diesel £1.55, a petrol car returning 42mpg over 12,000 miles will cost about £1,884 in fuel. A diesel returning 58mpg will cost about £1,458 — a saving of roughly £426 a year. But if the diesel costs £2,000 more to buy and you keep it three years, you’re barely breaking even before you factor in higher servicing, AdBlue, and potential DPF repairs.

Vehicle Excise Duty (VED) is now based on CO2 for the first year, then a standard rate. Most family petrols and diesels fall into similar bands. Company car tax favours petrol unless the diesel meets the latest RDE2 emissions standard. And residuals? Diesels are no longer the safe bet they once were, as buyers worry about future restrictions. Check these costs carefully:

• Purchase price difference between equivalent models.
• Real-world fuel economy and local pump prices.
• Servicing intervals, cambelt or chain costs, and AdBlue.
• Insurance group and likely repair bills.
• VED and company car tax.
• Expected depreciation over your ownership period.

Emissions, clean air zones, and making your choice

Diesel generally produces less CO2 per mile, which is why it was promoted for so long. But it emits more NOx and particulates, which are linked to respiratory problems. That’s why clean air zones (CAZs) and London’s Ultra Low Emission Zone (ULEZ) charge older, more polluting vehicles. Most Euro 6 diesels (roughly 2015 onwards) are compliant, but some zones still charge Euro 5 diesels. Petrol cars meeting Euro 4 (roughly 2006 onwards) usually avoid charges. If you drive into a city regularly, check the rules before you buy — a cheaper older diesel could cost you £12.50 or more every day.

So, what’s the verdict? Be honest about your driving. If you mostly nip around town and cover low miles, petrol is the practical, lower-risk choice. If you’re a motorway muncher with high annual mileage and a need for torque, diesel still makes financial sense. Test drive both, run the numbers with your own mileage and local fuel prices, and don’t forget to factor in future restrictions. Whichever you choose, keep up with servicing, use the correct oil, and drive gently when cold. A well-maintained car of either fuel type will serve you better than a neglected one.