Petrol prices may have plummeted over the past year but fuel still makes up one of the largest bills for car owners, with a litre weighing in at an average of 116.62p  – now more than diesel for the first time in 15 years.

Don’t think this means you have to give up petrol power and opt for a diesel in your search for cheaper fuel bills, however. LPG – liquefied petroleum gas – converted cars let you run a petrol car and benefit from fuel that costs a mere 57.31p per litre on average, with the option of running on standard petrol if you can’t find a forecourt selling LPG.

With lower emissions of nitrogen oxides than diesel and fewer particulate emissions than other fuels, LPG machines could be a more environmentally-friendly option, while the prevalence of LPG filling stations makes them a more viable option for many people than the current crop of electric cars. Thanks to the ability to fill one tank with petrol and a second with LPG, these machines practically double the range you can travel on one fill.

As a result, motorists could save up to 40 per cent on their fuel bills with LPG machines. There is a catch, though. LPG models aren’t on sale from mainstream car manufacturers, meaning buyers have to purchase a car and pay around £1,500 to convert it to run on LPG, while the addition of an LPG tank underneath the boot floor cuts the amount of space in the boot slightly. We tested a Ford Focus turbocharged 1.6-litre petrol converted by Autogas.

What is it?

This is an LPG converted version of one of the UK’s most popular cars, the Ford Focus. The model we tested is a pre-facelift 2014 model, which features a potent turbocharged 1.6-litre petrol engine (that Ford has since phased out, but which is widely available on the used market) and comes in sporty Zetec S trim.

The car looks the same as the standard petrol model, barring a small filling nozzle on the rear bumper, which accesses the LPG tank that sits under the boot floor. The interior, meanwhile, only differs from the standard car with the addition of an LPG-petrol switch and an LPG fuel gauge, located on the side of the centre console.

What is it like to drive?

The Ford Focus is famed for its sharp handling and impressive roadholding – and none of this is lost with the addition of LPG kit. With large alloy wheels and sports suspension the ride in our test car is firm, and larger bumps do make their way through to the cabin, but this is still a reasonably comfortable vehicle overall.

The petrol engine is also suitably punchy, offering strong pull from low engine speeds and providing impressive acceleration on the motorway. Considering the chance for cut-price fuel bills with this model buyers shouldn’t feel short changed in the power stakes. Switching between petrol and LPG is also very simple, with an easy-to-press fuel selector.

However, you won’t forget it can run on LPG, as the interior of our test car had a distinctive smell reminding you that the LPG tank sits underneath the boot floor. The engine also splutters a little when the automatic start/stop system fires the engine back up when you put the car back into gear. We also found the petrol gauge moves around quite a lot – even when running solely on LPG when it shouldn't be using any petrol.

What is it like inside?

The interior of the Autogas Focus is practically identical to that of the standard petrol car, with just the addition of an LPG switch and fuel gauge in the cabin, and an LPG fuel tank underneath the boot floor.

Our test car – which features a slightly different interior and exterior design to the new Ford Focus – features comfortable and supportive front seats and reasonable space in the front and rear seats, though the centre console layout is a little messy and hard to decipher on the move.

Is it practical?

The Autogas Focus is just as practical as the standard Focus, barring space in the boot. With a raised boot floor to accommodate the LPG tank, load carrying capacity drops a little, though the boot should be adequate for most buyers. Barring that and the slight smell of gas that comes with the addition of an LPG tank, there is not much to differentiate the practicality of ordinary petrol Focus models and the LPG version.

Should I buy one?

If you cover many thousands of miles every year and want a fast, cheap-to-fuel model, but would rather not have a less refined diesel, opting for an LPG model could make sense. With buyers able to save around 50p per litre on fuel with LPG, drivers who intend to keep their car for many years could be quids in by paying to convert their car to run on LPG.

Around 25,000 miles use should see the LPG kit beginning to pay for itself, so if you plan on driving your car for more than this distance before replacing it, paying the £1,500 needed to convert a Ford Focus like our test car could be a wise move.

However, as a modified model, our test car didn’t feel as well engineered as the standard Ford Focus, with a mild smell of gas inside the car and a start/stop system that seemed to splutter a little when firing up again on LPG power.

Don't want to buy new? You can browse for a used Ford Focus in our classifieds here.

The facts

Autogas Ford Focus 1.6 EcoBoost LPG conversion

List price: £1,500 
Engine: 1.6-litre, turbocharged four-cylinder petrol
Power: 180bhp
Top speed: 139mph
0-62mph: 7.9 seconds
Fuel economy: 47.9mpg (combined)
Emissions: 137g/km CO2
Euro NCAP rating: Five-star

Picture: Ford