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Around one million cars that are currently on the road cannot use a type of petrol that will become standard at petrol stations around the UK, and will be forced to pay more for their fuel or face damaging their car.
As it stands, petrol stations in the UK tend to dispense a fuel known as E5, which is a mixture of petrol and five percent bioethanol.
That's because it's better for the environment than having everything run on 100 percent petrol.
However, in September there's going to be a change, and pumps will start dispensing a new fuel called E10.
It's called E10 because - you've guessed it - it contains 10 percent bioethanol instead of the previous five.
This is because of a government scheme to make petrol cars a bit more environmentally friendly by making them produce less CO2, therefore slowing the effects of climate change.
Now, if you own a car that was made after 2011, you're going to be OK. They all take this sort of fuel just fine.
Many cars from the late 1990s are the same.
However, there are some that were built in the middle of that time period that aren't.
Approximately five percent of vehicles, if the government's figures are correct.
Of the 32.7 million cars currently on UK roads, 18.7 million run on petrol.
That means that there are about 935,000 that will be incompatible with E10.
There are also 1.27 million motorbikes, of which nearly all run on petrol, meaning that about 63,500 are going to be affected.
If you want to check, there is a government website that you can run your car's model, engine size, and manufacture year through to see if it's going to be OK.
However, the website warns: "DfT and its partners will not be liable for any damage to your vehicle as a result of you using this service.
"It's your responsibility to make sure you use the right fuel for your vehicle."
If you've a pre-January 200 Citroen, you might want to double check, because they're incompatible.
Same goes for Nissans of the same age, and Ford Mondeo 1.8 SCI cars built between 2003 to 2007.
If you find you've a car that won't take it, don't worry about it too much.
E5 fuel will still be sold, it'll just be more expensive.
If you find yourself in a really tight spot, you can stick it in the car and it'll go, but consistent use will lead to engine damage, so you'll want to reduce that chance.
Furthermore, E10 is slightly less efficient than E5, meaning you might see around a one percent fall in the amount of miles to the gallon you get, according to the government.
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