We’ll forgive you if you’re not a regular visitor to the website of Berlin’s International Council on Clean Transportation. It isn’t in my browser's favourites bar either.

The only reason I know of the body’s existence is because a BBC radio news report I heard, in which a UK academic referenced a recent ICCT study with some rather alarming results.

Last year, the ICCT strapped portable emissions measurement systems like the ones used by our own True MPG economy testers to 15 new Euro-VI-emissions-compliant diesel production cars. It discovered that, in real-world driving, the cars’ emissions of nitrogen oxides were seven times higher than they should be. And that’s on average, by the way; not in a worst-case scenario. And not by a factor of two or three, or something else that could perhaps be explained away; seven times.

‘NOx’ being one of the nastier things your tailpipe can produce – linked specifically to smog formation in cities and respiratory problems – that’s certainly enough to make you question whether modern diesel combustion technology is developing quite as quickly as the car-makers are telling us.

The question is, what should you do instead? In what’s become a pretty savvy context into which to sell alternatively fuelled new cars – where people query the real-world economy of hybrids, the true well-to-wheel sustainability of national grid powered EVs and PHEVs, and in which an affordable hydrogen fuel cell car remains a distant prospect – what fuel do you choose now if you want to be responsible?

Elsewhere in Europe, the answer’s LPG. Liquid petroleum gas produces 90% less NOx than diesel, 40% less of it than petrol, and much less particulate matter than diesel too. It makes less CO2 than both conventional fuels on a well-to-wheel basis too, on account of LPG being a by-product of the world’s crude oil and natural gas industries.

Until a decade ago or so, a handful of UK car distributors offered LPG versions of their petrol models, but in 2005 the UK government wound up its Powershift grant scheme, via which you could get up to three-quarters of the extra cost of your LPG car back from the exchequer.

Since then, the case for running an LPG car in the UK has made more ideological sense than pecuniary – and after a test this week of a Ford Focus converted for the fuel by LPG distributor Autogas, I can regrettably confirm that’s still the case. For now.

The option can be all-but ruled out for buyers of new cars straight away, there being no UK market availability of the LPG-fuelled models that are offered elsewhere. Converting a nearly-new petrol car for the fuel could well be to save up manufacturer warranty problems for later, and I wouldn’t recommend it.

If you’re buying used, the savings are there in principal – but for the majority of drivers they probably wouldn’t be great enough to justify the effort and risk. Autogas claims that its LPG Focus, based on a 1.6-litre Ecoboost petrol, costs 10p-a-mile to fuel, compared with 12p for the equivalent turbodiesel and 14p for the normal petrol. For me, the demonstrator returned 33mpg in mixed used running on LPG, and 38mpg running on unleaded.

But given that a litre of LPG currently costs about 60p, shouldn’t that leave everyone quids in? Not quite. Because of the way Autogas’ conversion kit works, the car starts from cold on unleaded, and uses it sporadically throughout the normal combustion process. So for every five 51-litre tanks of LPG you use, you’ll get through roughly a tank of unleaded as well.

To cut to the chase, a typical UK driver doing 10,000-miles-a-year would save almost £400-a-year on fuel by switching from unleaded in his Focus Ecoboost to LPG. Plenty of people cover more miles than that, of course. But given that a typical LPG conversion currently costs £1400, they’d need to do a lot more miles than that in order to start saving money in reasonable order – particularly relative to a modern 65mpg economy diesel.

It’s a shame because, in day-to-day use, LPG’s probably now 95 per cent as good as petrol in your engine. The increasing prevalence of direct injection and turbocharging technology has reduced the performance deterioration inherent in an LPG conversion to the point where, in the Focus demonstrator at least, the gap’s barely noticeable.

Refinement’s on a par, power delivery’s unaltered. The only way you really know you’re running on LPG at all is by a slightly woolly feel to the accelerator pedal; the occasional bit of lumpiness to the combustion on transient throttle; and by an apparent minor reduction in engine braking.

Autogas claims there are now 1400 places to fill up with LPG across the UK, so fuel availability can hardly be considered an obstacle. It’s calling for the government to rectify its long-standing discrimination against LPG – and if it does, reinstating the subsidy it used to offer (which is a fraction of what it currently hands out for a PHEV or EV), I wouldn’t be at all surprised to see the fuel make an unlikely comeback.

In fact, if EU mandarins are serious about making real-world testing a part of their forthcoming new emissions legislation, and their UK counterparts wake up and make NOx an equal influence on car tax as CO2, such a comeback’s quite a strong possibility.

The World Light Test Procedure, which is expected to replace the New European Driving Cycle’s ‘Euro-X’ emissions standard before the end of this decade, could yet mark the beginning of the end for ever-more-complex turbodiesel engines in passenger cars. If it does, LPG could be a ready-made replacement.