THE dual incentives of reduced running costs and lower emissions is inspiring more and more motorists to look for alternatives to both diesel and petrol powered cars.

For many that means buying electric cars or at the very least hybrids, which run on a combination of both petrol and electric.

In both cases there are drawbacks, however, not the least of which is the initial cost. And in the case of electric-powered vehicles range can be an issue.

Hydrogen could be the way forward but for many, hydrogen cars are at present well outside their price range. Toyota's recently announced Mirai, for example, has a price tag of £66,000.

But there is a fuel which has been saving drivers thousands of pounds for a number of years, but which to some extent has slipped off most people's radar. And that's Liquid Petroleum Gas, or LPG.

Borrowing an LPG-powered Ford Focus 1.6-litre EcoBoost from LPG specialists Autogas I took a fresh look at the fuel which it's claimed is 40 per cent cheaper for the average motorist than using petrol and around 30 per cent cheaper than diesel.

And a trip to the pumps showed me why. For while unleaded petrol is now hovering around £1 a litre LPG is just 59p.

Now admittedly you get fractionally less miles per gallon with LPG but the price differential is so dramatic more and more people are doing the maths.

For starters you need a conventional petrol car which is then converted to run on LPG for a cost of between £1,200 and £1,500.

A spokesman for Autogas told me most motorists found the saving in fuel costs enabled them to recover the conversion cost is around 12-18 months - depending upon their average mileage - after which you are saving money every time you fill up.

Because the LPG tank tends to be fitted beneath the boot floor you can - depending upon your model of car - lose some luggage space but in most cases the loss is very small.

Unlike charging points for electric cars there's now no real shortage of garages selling LPG. In fact there are 1,400 of them in the UK, including one Shell station in every four.

But even if you are in an unfamiliar area there's no problem as the cars retain their petrol tanks and if you run out of the liquid gas the system just switches seamlessly to run on petrol.

In fact petrol is used as the initial fuel each time you start your car, with the switch to LPG happening after just a few minutes when the engine gets warm.

I found that on the first start up in the morning the switch over happened after around a mile to a mile and a half of travel. On subsequent start-ups the distance would be less than half of that.

If you don't look at the lights which tell you whether the car is running on petrol or LPG, however, you wouldn't know as it feels exactly the same whichever fuel you are running on.

So if you are considering making the change you won't have to worry about any loss of performance - it's just down to how much money you will save.

Filling up is straightforward if slightly different. Having put the nozzle into the LPG tank you pull the trigger and lock it open before pushing a button on the pump itself to release the fuel. Bizarrely if you release the button and press it again to add a little more fuel the counter returns to zero and then starts running again so you have to add the two totals together, although the final bill is the same.

The LPG tank on the Focus will take 51 litres while the petrol tank can accommodate 58 litres. Running on petrol the car's CO2 emissions are 137 grams per kilometre but on LPG there is a reduction of 12.5 per cent.

And Autogas says there are up to 98 per cent fewer harmful particulates in the emissions from LPG than other fuels so you have the satisfaction of knowing you are helping to keep the air we breath cleaner.

That's just one of the reasons the company is currently working with its conversion centre in Harborne, Birmingham and the city council to convert 80 black cabs in the city to run on LPG. The results will be closely watched by all other major cities around the UK.