Diesel’s days certainly look like they’re up if the media is anything to go by, examples including inews.co.uk reporting that “Diesel and petrol cars ‘must be banned by 2030’” and the Evening Standard revealing that “Petrol and diesel cars are banned from east London roads to tackle toxic air”.

Influenced by ironic opposition from many European governments including the UK’s, along with the resulting effect on public consumer sentiment and the unarguable impact diesel emissions are having on health including a young girl’s death being attributed to air pollution, car manufacturers are increasingly dropping the fuel.

Manufacturers’ moves

Autocar brought the news in August that ‘Subaru axes diesel engines from its model line-up’, while CarAdvice revealed this week that ‘Peugeot [is] no longer investing in diesel engines’.

Car brands are not all taking this route, though, as mainstream manufacturer ‘Ford adds new diesel engines to S-Max and Galaxy MPVs’. Bosch, which manufactures a bewildering array of car parts for various popular models, is busy developing technology to drastically reduce diesel vehicles’ NOx emissions, to match their already comparably attractive CO2 emissions compared to petrol equivalents.

Viability depends on body-style

Diesel is quickly dying in the supermini/city car segment, though – and rightly so. Dieter Zetsche from Mercedes spoke to Autocar at this month’s Paris motor show and explained why diesel doesn’t make sense for small cars, but believes in reference to cars of hatchback size like the A-Class and above that “for bigger cars, there is a bigger difference and you don’t need to change diesel.”

The environmental irony of it

October began with ‘Diesel prices hiked for 13th consecutive week’ as reported by Aol, but anyone rejoicing because dirty, smelly diesel vehicles are being discouraged from the UK’s roads to the benefit of the environment should think again. While levels of harmful nitrogen oxides and particulate matter may indeed reduce by ditching diesel, the UK’s CO2 emissions have risen for the first time in 14 years, which feels like a backward step in certain respects.

While studies and tests have shown that, for instance, “80% of diesels [are] in breach of emissions limits”, the petrol vs diesel debate is as clear as mud, the climatic benefits of each fuel resulting in something of a seesaw.

Business fleets

As a contract hire, car/van and leasing company, we have a lot of contact with fleet managers – and a new report from the AA and BT has found that they’re “frustrated with ‘dirty’ diesel rhetoric” and of the 500 fleet managers surveyed, diesel continues to be their first choice for cost and practicality reasons.

Which? fuel to choose?

The August 2018 issue of Which? magazine looked at the pros and cons of diesel, petrol and hybrid cars including mild, conventional and plug-in variations, weighing up the latest models against the publication’s strict in-house test programme – and the results are eye-opening.

As a general rule of thumb for anyone considering leasing a car on personal contract hire, diesel isn’t worth entertaining for superminis, convertibles, compact estates, people who rarely drive with more than two people on board and those who cover under 20,000 miles per year. For motorists who spend a large chunk of time tearing up and down the UK’s motorways, diesel can still prove the most sensible choice.

A mixed bag of results

Under Which? magazine’s newest and more realistic test programme, it was found that the 46 diesel cars rated all produced, on average, almost four times the amount of NOx that is permissible under the latest Euro 6 emissions rules. Subaru’s Forester in diesel guise performs significantly more grimly, though, pumping out 25 times the official NOx levels in Which?’s tests despite the 2.0-litre (147PS) Boxer diesel engine’s attractive credentials on paper of 49.6mpg and 148g/km CO2 emissions despite being underpinned by Subaru’s Symmetrical All-Wheel Drive system. Diesel models from French car manufacturer Renault also came out poorly in the publication’s ‘dirtiest and cleanest’ comparison of the cars available to them, while Mercedes’ E-Class and S-Class performed commendably.

When it comes to petrol models that Which? tested, the worst CO2 culprit bizarrely came out as the Ford Ka+, while other popular personal lease models like the Audi Q2, Fiat 500 and SEAT Leon also appeared in the top ten.

A conventional petrol hybrid model, the Kia Niro, also made the list, producing over three times the cited CO2 emissions. This rekindles memories of the week we spent independently road-testing a Niro and averaged in the high-40s compared to its brochure figure of 74.3mpg despite driving it unladen and very carefully with economy in mind at all times.

Hybrids require a different driving style to eke the most out of their potential, which not all drivers will be able to get used to. Instead of accelerating away from junctions slowly, which usually encourages healthier MPG figures from petrol and diesel models, it’s actually often best to be firmer with the throttle when driving a hybrid, reaching the target speed more briskly then taking one’s foot off the accelerator to allow regenerative braking to start recharging the battery.

Hybrids are improving fast

Motorway ‘MPG’ tests unsurprisingly saw a diesel top the chart, with the Mercedes CLA Shooting Brake (estate) averaging in the mid-50s and the Mazda3 hatchback nudging 50mpg. Less predictably, though, the second best car for motorways according to Which? is the Toyota Prius conventional (not plug-in) hybrid, defying the fact that hybrids have traditionally performed poorly on motorways compared to diesel equivalents.

The ‘around town MPG’ results are much more expected, however, with three Toyota hybrid models plus Hyundai’s Ioniq in hybrid guise also finishing in the top five, propped up by Suzuki’s excellent little Celerio – the car in which our editor Oliver finished in joint first place alongside former Top Gear presenter Sue Baker in an MPG challenge event. After winning an enormous block of Cheddar at the launch down in Somerset, it took him a whole week of cheese sandwiches and pasta bakes to polish it all off.

The overall winner of Which?’s realistic test programme was actually the Volkswagen Golf GTE (in estate form to be specific) with 74.3mpg, which doesn’t come as a surprise to us as it continues to prove extremely popular in the business and personal contract hire (PCH) markets thanks to blending premium quality and punchy performance with appealing overall running costs. For an estate car of this size, the study’s annual running costs figure of £270 certainly is attractive compared with internal combustion engines i.e. conventional petrol and diesel. Only one diesel model, the Mazda3, appeared in the top 5 overall MPG winners.

Powertrains’ exciting future

Ironically, Mazda plans to release a diesel-hybrid SUV in 2020, not just in Asia and across Europe including the UK but also in America where thirsty petrol beasts still dominate. It looks set to be a mild hybrid with a diddy 48V battery and compact electric motor, which is the trend many manufacturers like Audi are following. Although Mazda has pledged to electrify its range by 2030, the Japanese firm has excitingly revealed plans to revive its legendary Wankel rotary engine perhaps as early as 2020 and forming a hybrid powertrain, as part of its interim EV strategy. Mazda also ‘wants to perfect the internal combustion engine before we give it up’ and its new SkyActiv-X petrol engines are said to combine ‘the efficiency of diesel with the cleanliness of gasoline.’

Diesel, petrol or hybrid: all things considered

Congestion zones are increasingly being mooted for many of the UK’s cities and some towns, but viewing things realistically, Oxford doesn’t look likely to ban all non-zero-emissions vehicles until 2035, and London’s T-Charge doesn’t apply to the latest Euro 6 engines that feature in the majority of new models. Leasing a car, of course, always means a brand new vehicle and hence poses less of a concern than someone buying a used or ‘nearly new’ ex-demo car.

Summing up, diesel is still usually the best fuel for people who tow caravans, trailers and the like, and for long-distance drivers who cover around 20,000 or more miles per year mainly on motorways. Luxury saloons like the Mercedes E-Class and BMW 7-series are often found to still perform impressively in the environmental and economy stakes, too.

For everyone else, though, hybrid cars are shaping up to be the most attractive prospect, presenting a good case for bypassing petrol entirely. While plug-in iterations require more discipline when it comes to nightly charging, conventional hybrids are improving all the time. It’s just a shame that slightly larger petrol tanks aren’t fitted as a general rule, saving more frequent forecourt visits than drivers of remarkably parsimonious VW 2.0 TDI engines, for example, will be used to.

It pays dividends to read as many road-test reviews as possible, though, along with visiting and perhaps joining owners’ club forums, rather than taking manufacturers’ claimed figures as gospel. Real-world findings from actual motorists are worth the extra research time to ensure the right car and right fuel are chosen for the circumstances.

Only history will determine what will happen if car CO2 emissions keep on rising after years of hard work reducing them, but the new WLTP emissions test and rising diesel pump prices combined with national and local policies plus public sentiment won’t slow diesel’s imminent death – making now the ideal time to take the plunge and embrace hybrid power.

Our knowledgeable leasing team will be happy to provide no-obligation and impartial advice for those looking to make the switch to hybrid cars.