New E10 fuel could spell damage to hundreds of thousands of older cars

If so, you might want to think carefully before filling up at the petrol station. From this month, the 'standard' unleaded petrol on sale – as opposed to the more expensive 'premium' product – will be replaced with a 'greener' alternative, made up of 10 per cent bioethanol. But while the new petrol might be good for the planet, it could spell disaster for drivers of older cars.

For the majority of drivers this will not be an issue. Legislation means that all new cars built over the past 10 years should be ready for the new 'E10' petrol, and the Department for Transport estimates that 95 per cent of cars on the road will be unaffected.

But that still leaves a sizeable minority, thought to be at least 600,000, of older cars on the road which are not compatible with the new fuel. A one-off mistake should not be a disaster, providing you do not allow it to fester in your tank, but long-term exposure could do lasting damage to expensive rubber seals, plastics, and most crucially, fuel lines.

So what is E10 petrol, and why is it being introduced?

Up until this month, standard unleaded fuel on most forecourts was made up of 95 per cent oil-derived petrol, and five per cent ethanol, hence the E5 designation. But from this month onwards, ethanol content in standard petrol will be doubled to 10 per cent.

The ethanol used in petrol is a 'biofuel', made from sources such as sugar cane. The Government hopes that switching to E10 will cut carbon dioxide emissions by 738,000 tons a year, the equivalent of taking 350,000 cars off UK roads.

But it also admits that the new fuel will "marginally" reduce fuel economy, although it insists the impact is "almost unnoticeable to most drivers when making everyday journeys".

A major area of concern is among owners of 'classic cars' which will in many cases not be compatible with the new fuel.

Jeff Ruggles of Classics World magazine says: "There are two big issues with ethanol fuels and older cars. "The first is that ethanol can have a corrosive effect on metal, plastic and rubber parts in the fuel system.

"The results of this can range from the inconvenient, like sticking carburettor floats, to the dangerous when fuel lines perish."

Not all vehicles will suffer such problems, he says.

"Rather like the introduction of unleaded fuel back in the 80s, some will be perfectly happy on the new fuel and some will need modification."

But he says the second issue, which will have a particular bearing on classic cars, is that ethanol has a tendency to absorb water.

"Clearly the longer a car is left standing idle, the bigger an issue this will be, with any moisture in the fuel only adding to potential issues."

Owners of older vehicles are advised to use 'premium' or 'super' unleaded petrol instead, which typically costs about 40p a gallon.

Transport Secretary Grant Shapps says: "Every journey matters as we drive forward the green industrial revolution, which is why the roll-out of E10 is so important.

"It'll help us cut road greenhouse gas emissions and meet our ambitious net zero targets.

"Although more and more drivers are switching to electric, there are steps we can take today to reduce emissions from the millions of vehicles already on our roads.

"The small switch to E10 petrol will reduce greenhouse gas emissions as we accelerate towards a greener transport future."

The move has been broadly welcomed by AA president Edmund King.

He says: "This is a positive and simple step to help reduce the carbon impact from road transport.

"While the vast majority of vehicles will be unaffected by the change, it is important for owners of older cars to use the Government's vehicle checker to see if they can use E10."

But not everyone is impressed. Greenpeace reckons the switch will do more harm than good to the planet, saying that turning land over to the crops to produce the ethanol in petrol will outweigh any environmental benefits.

The Government says that all larger petrol stations will be required to supply super unleaded for at least the next five years, when the matter will be reviewed, although smaller filling stations will not be required to follow this.

And what happens if you mistakenly put E10 fuel into a car that is not compatible?

Mr King says there is no need to panic: "Simply put super unleaded in their tank at the next available opportunity."

To see if your car is compatible with the new petrol, see the government vehicle checker: gov.uk/check-vehicle-e10-petrol