Petrol or diesel is still one of the first questions most UK buyers face, even with electric and hybrid cars taking a growing share of the market. Petrol accounts for roughly 47% of new car sales, and diesel remains a genuine, sensible choice for plenty of drivers, particularly those covering serious motorway miles.
Neither is objectively better than the other, the right answer depends almost entirely on how you actually drive.
This guide walks through the real differences, purchase price, running costs, emissions, performance and longevity, so you can work out which one genuinely suits you rather than just following general advice that might not apply to your situation.
Summary:
- There's no universal answer, only the right answer for your driving pattern. Diesel suits long motorway journeys and towing, petrol suits shorter, urban driving.
- Diesel produces less CO2 per kilometre but more NOx, the pollutant most harmful to human health in built-up areas. The RAC puts average UK diesel emissions at 173g CO2/km against 143g for petrol.
- A well-maintained diesel can genuinely outlast a petrol engine, some running to 500,000 miles or more, thanks to lower running speeds and a naturally tougher build.
- The 2030 and 2035 bans apply only to new car sales, not used cars, so buying a used petrol or diesel car remains entirely unrestricted for the foreseeable future.
- If you're buying to drive in London regularly, an older diesel specifically faces the steepest ULEZ costs, since the cutoff for compliance sits at September 2015.
Purchase Price
Diesel cars typically cost more to buy than an equivalent petrol model. The engines themselves are built tougher to handle higher compression, and they come with extra emissions equipment, a diesel particulate filter and an AdBlue system, that petrol engines simply don't need. That higher purchase price is the first thing to weigh against any fuel savings you're expecting further down the line.
Running Costs
Diesel generally wins on fuel efficiency, especially on longer, steadier motorway journeys, and that can offset its higher purchase price over time. Whether it actually does depends heavily on how many miles you cover.
The average UK driver covers around 6,082 miles a year, and at that kind of mileage, the fuel savings from diesel often don't outweigh the higher price paid upfront and the extra maintenance costs involved.
Diesel servicing and repairs also tend to cost more, largely because of that extra emissions equipment, and AdBlue itself needs topping up every few thousand miles, a small but real ongoing cost.
Emissions and Tax
This is where the picture gets genuinely more complicated than most buyers expect. Diesel produces less CO2 per kilometre than petrol, the RAC's figures put the UK average at 173g CO2/km for diesel against 143g for petrol, since diesel's fuel efficiency means less fuel burned per mile overall.
But diesel produces considerably more NOx, nitrogen oxide, the pollutant most directly linked to poor local air quality and respiratory harm, particularly in slow-moving, stop-start city traffic. The Royal College of Physicians estimates air pollution is linked to around 30,000 UK deaths a year, and diesel emissions are considered a significant contributor to that figure specifically in urban areas.
Road tax banding depends on whether your car meets the Real Driving Emissions 2 (RDE2) standard, which sets maximum NOx limits, cars that don't meet it pay a higher first-year rate regardless of fuel type.
Driving and Performance
Diesel engines run at lower revs but deliver considerably more torque, genuinely useful for towing or carrying heavy loads, and they've become noticeably quieter and smoother than older diesels used to be. Petrol engines feel livelier at higher revs and remain the quieter, more refined choice for most everyday driving, without the occasional low-speed "clatter" some diesels still have.
Does Diesel Really Last Longer?
Generally, yes. Diesel engines are built to handle much higher compression than petrol engines, and they typically run at lower RPMs, both of which mean less wear over time. Diesel fuel also carries natural lubricating properties that help internal parts last longer.
A well-maintained diesel can genuinely reach 500,000 to 1,000,000 miles, figures a petrol engine essentially never approaches, though a well-looked-after petrol engine will still comfortably outlast most owners' actual ownership period regardless.
What About the 2030 and 2035 Bans?
The UK government has reinstated its target to end sales of new petrol and diesel cars by 2030, with a full ban on new hybrids too from 2035, after which only zero-emission vehicles can be sold as new, a change that genuinely doesn't affect used cars at all.
There's currently no restriction on buying or selling a used petrol or diesel car, and that isn't expected to change any time soon, though it's worth knowing this is the long-term direction the market's heading when you're weighing up how long you plan to keep a car.
Petrol vs Diesel: Quick Comparison
| Factor | Petrol | Diesel |
|---|---|---|
| Purchase price | Generally cheaper | Generally more expensive |
| Best suited to | Short, urban journeys | Long motorway trips, towing |
| CO2 emissions | Higher per km (143g average) | Lower per km (173g average, but more fuel-efficient overall) |
| NOx emissions | Lower | Higher, worse for local air quality |
| Servicing costs | Generally lower | Generally higher |
| Typical longevity | High with good maintenance | Genuinely higher, up to 500,000+ miles possible |
| ULEZ/low-emission zone risk | Lower | Higher for pre-September 2015 models specifically |
Buying to Drive in London?
If you're planning to drive regularly within Greater London, this decision genuinely matters more than it might elsewhere. Diesel cars registered before September 2015 don't meet ULEZ standards and face a £12.50 daily charge, while non-compliant petrol cars specifically need to predate 2006.
For the full detail on what qualifies and what doesn't, see our guide on ULEZ compliant cars explained.
Conclusion
There's genuinely no single right answer here, only the right answer for your specific driving pattern. If most of your driving is short, urban trips, petrol remains the simpler, cheaper, more sensible choice.
If you're regularly covering long motorway distances or towing something heavy, diesel's efficiency and torque still make genuine sense, provided you're comfortable with the higher purchase price and servicing costs that come with it.
Whichever you choose, buying used sidesteps the sharpest edge of this decision entirely, since the 2030 and 2035 bans only affect new sales, not the car you're actually looking at today.
Frequently Asked Questions
Is it worth buying a diesel car if I only drive locally? Generally not. Diesel's efficiency advantage shows up on longer, steadier journeys, and short, stop-start trips can even cause its diesel particulate filter to clog over time, an extra maintenance headache petrol simply doesn't have.
What happens if I put diesel fuel in a petrol car? The engine will likely misfire, smoke, or fail to start, since diesel doesn't combust the way a petrol engine needs it to. Don't start the engine if this happens, and have the tank drained before attempting to drive.
What happens if I put petrol in a diesel car? This can genuinely damage the engine and fuel system, since petrol lacks the lubrication diesel engines rely on. Don't start the engine, and have the car towed for a professional fuel system flush instead.
Does the fuel type affect my car insurance? It can, indirectly. Diesel's extra emissions equipment tends to cost more to repair, which can feed into a higher premium, though your age, address, driving history and the car's overall value all matter considerably more.
Will the 2030 ban stop me buying a used petrol or diesel car? No. The ban applies only to new car sales, buying a used petrol or diesel car remains completely unrestricted, and that isn't expected to change in the foreseeable future.
