There are black clouds gathering above diesel cars - both figuratively and literally. Should you be worried if you own a diesel car, and should you think again if you're planning to buy one?
Recent news headlines have once again called the emissions levels of diesel cars into question. The results of a Government survey yesterday showed that in real-world testing, no diesel car could meet the upper limit of nitrous oxides (NOx), which is based on testing in a laboratory.
But what does all this mean for the consumer? Should you still buy a diesel car? Or should you buy a petrol car instead? Or indeed, is now the time to ditch the old ways, and instead go shopping for a hybrid or electric car?
Here's the latest on the emissions row, and what you need to know if you're planning to buy a new car.
What's happened so far?
In September 2015, it was revealed that the Volkswagen Group had used special devices known as "defeat devices" in order to cheat on emissions tests in the USA. This sparked a flurry of reaction from legislators around the world, with our own government launching an investigation into emissions.
The results of that investigation were revealed yesterday, with confirmation that their own tests "have not detected evidence of test cycle manipulation strategies as used by the Volkswagen Group".
However, the investigation did officially confirm something that many industry commentators have known for a long time, which is that in the real world, no car produces emissions as low as it does in the laboratory tests, and furthermore, a great many cars produce far more emissions out on the road.
That doesn't mean manufacturers have been cheating per se, but that they've been producing cars which perform well in the extreme lenient test scenario, and that those readings have little bearing on what the cars produce out on the road, in normal use.
What about other car manufacturers?
In Germany, authorities have today told journalists that several manufacturers - three VW group marques (VW, Audi, Porsche) plus Mercedes-Benz and Opel, Vauxhall's German counterpart, are to effect a voluntary recall in order to update the software in their cars to reduce their NOx emissions.
In addition to these car makers, the German transport minister, Alexander Dobrindt, has since confirmed that the German government's official investigation into the VW emissions scandal has revealed "irregularities" in cars from 11 other manufacturers: Renault, Alfa Romeo, Chevrolet, Dacia, Fiat, Hyundai, Jaguar, Jeep, Land Rover, Nissan and Suzuki.
It's thought that some diesel models' exhaust gas re-circulation systems have been kicking in only above a certain temperature limit, in order to preserve the life of the engine below those temperatures. The side-effect, of course, has been exhaust emissions that were significantly higher when the temperature was lower.
The mechanisms under the spotlight in this case have no relation to those used in the VW cheating scandal, although this latest recall could have repercussions in the UK, as it may mean some cars' engine management systems will have to be re-designed, or even that some cars already sold in the UK will have to be recalled. We'll bring you more information on this as we get it.
In a statement, Vauxhall told us: "As announced on December 15, 2015 and explained in more detail on March 29, 2016, Opel/Vauxhall will start an initiative to improve NOx emissions of SCR (Selective Catalytic Reduction) diesel applications in new vehicles in August. Our offensive also includes a voluntary customer satisfaction field action that will involve Euro 6 SCR vehicles that are already on the road in Europe. This activity will start in June 2016."
In other words, it says it's planning a pre-emptive software update on certain models in order to reduce their NOx emissions, even though it hasn't been ordered to by the authorities. Vauxhall also told us that 57,000 cars across Europe would be called in for the software update, which suggests a figure of around 16,000 cars in the UK. Affected models will include Insignia, Zafira Tourer and Cascada cars with the 2.0-litre 170 diesel engine.
Mercedes-Benz is offering something similar on its V-class model, as well as certain compact cars with Renault-sourced engines. "There are technical reasons for deviations from the certified norm values, as is the case in other tests as well," it said in a statement.
"We will offer customers of our compact cars and the V-Class an improvement of their cars' emissions behavior on a voluntary basis. The entry-level engines of our compact cars include one engine variant from Renault (OM 607) in the context of our cooperation with Renault.
"That engine from Renault is adapted to the requirements of our Mercedes-Benz compact models. We have been informed about the software update by our cooperation partner and will of course offer this service to our customers on a voluntary basis. As a result, we will achieve a significant improvement in emissions this year."
So does all this mean I should avoid buying a diesel car?
It's really up to you, and depends largely on your feelings on the environment. The gas that diesel cars emit more of is NOx, which can cause health problems for people who breathe it in; most notably, lung and breathing problems, eye irritation and headaches.
Diesel cars also emit particulates, which are microscopic solid particles that can embed themselves in the lungs, also causing breathing problems and even lung cancer.
All of which sounds like reason enough to switch back to petrol. But the problem is, petrol cars are no saints, either. They emit higher levels of carbon dioxide (CO2), which has less fewer immediate health issues than NOx, but is a greenhouse gas which causes huge problems for the environment at large. Diesel cars, on the whole, emit less CO2 than petrols.
So, assuming an electric car won't work for you, deciding what to buy next is really a case of working out the lesser of two evils.
What about resale values?
Despite all the concern following the Volkswagen emissions scandal, there's actually been very little effect on the residual values of diesel cars as a whole. It remains the case that they're still more expensive to buy than petrol cars, but equally hold that extra value so that you get more back for them when the time comes to sell.
That could change in the future if people do start to move away from diesel in great flocks, but as yet we haven't seen any sign of that happening - indeed, at the moment it looks as though most buyers vote with their wallets, valuing the better fuel economy of a diesel car over any environmental concerns.
I already own a Volkswagen, Audi, Seat, Skoda or Porsche. Will it be recalled?
If you own one of these cars, you should have been made aware already by post if it will need to be recalled. In other words, if you haven't received a letter yet, the chances are your car's in the clear. If you're in any doubt, a phone call to your nearest VW dealer should clear things up.
My car has been recalled. Will I lose out?
Probably not. Volkswagen has been tasked with finding fixes in all the affected cars which don't cause any reduction in fuel consumption. As a result, when your car has had the fix applied, you shouldn't notice any change in fuel economy, and VW has even said the fix may well make its cars even more efficient than they were before.
Will VW buy back my car?
Probably not. If the company implements the fixes it's planning, then the cars involved will have their emissions brought into line with European limits. Therefore it would have fulfilled its obligations, and there would be no legal reason for which they'd have to buy back the cars.
The reason they've had to in the USA is because the limits are lower, which means it would have cost more for VW to reach them - making buying back the cars a simpler and more cost-effective way to fulfil its obligations.
Is the Government about to add extra tax to diesel cars because they're environmentally unfriendly?
There's certainly chance that this could happen in the future; certainly, there's been a lot of rhetoric about the environmental unfriendliness of diesel cars in recent months which could be a sign that the Government is gearing up to penalize these models.
However, it's extremely unlikely that it'll be able to apply any taxes or penalties retrospectively. That means if you're buying a new diesel car now, it's highly unlikely you'll be affected by any future policy changes.
That said, it's worth noting that in 2017, the car tax rules are changing, and while they won't penalise diesel cars, they will make it a lot less financially beneficial than it is right now for private buyers to own cars that emit less CO2.
In other words, while the tax on diesel cars isn't about to go up, petrol cars will cost less to tax by comparison, which means there'll soon be less of a financial incentive to own a diesel car.
So, it's OK to buy a diesel?
Notwithstanding the environmental issues we've already discussed, the advice remains the same as it was before: you should only buy a diesel if you really need one.
Many buyers simply assume that they'll save money by buying a diesel thanks to its better fuel consumption figures, when that isn't always the case.
Often, diesel cars cost more to buy, as does the fuel - although in recent years, the gap between petrol and diesel prices has narrowed.
Throw in the fact that modern diesels, which have lots of emissions control equipment fitted to them, frequently need expensive repairs further down the line when that equipment needs repair or replacement, and it's easy to see how those savings can quickly be wiped out.
You should also keep in mind the threat that diesel cars might become less and less desirable as the emissions stories continue to surface, too. Although we've seen no evidence of this so far, if diesel cars gain a reputation for being dirty and unhealthy, we could see residual values start to slide, making it even less financially viable to buy a diesel car.
For the time being, however, a diesel can still be cheaper to run than a petrol - but only if you're doing enough miles to justify it. And the only way to find out whether that's the case is to sit down and do some sums yourself.