New greener petrol being introduced across Britain by 1 September – but 600,000 vehicles are incompatible and it could push up costs

We've a full Q&A on what's happening and how it impacts motorists below. It comes as petrol prices recently hit their highest level since 2013, according to figures from the AA. For tips on how to cut petrol costs and improve fuel efficiency, check out our Cheap petrol and diesel guide.

What type of unleaded petrol is sold in forecourts now, and how is it changing?

There are currently two main types of unleaded sold in UK forecourts:

• E5 (95 octane) – this will disappear from most forecourts by 1 September. This is the standard unleaded petrol sold, though it's sometimes confusingly referred to as 'Premium'.

  It's being scrapped in most places in England, Scotland and Wales by 1 September as it's not considered green enough. It contains up to 5% of a substance called 'renewable ethanol' – made from materials such as grains, sugars and waste wood. But the Government wants to increase the concentration of this in petrol (which is happening with E10) as it means less fossil fuels are used in production.

• E5 Super (97+ octane) – this is staying put after 1 September. Despite E5 sometimes being referred to as 'premium', E5 Super is actually the premium version. It also contains up to 5% renewable ethanol, but is being allowed to stay as an alternative for vehicles that aren't compatible with the new E10 fuel. However, it's pricier than other versions.

But a big change will come in by 1 September when the majority of forecourts in England, Scotland and Wales will have to sell the following unleaded fuel instead of E5 (many forecourts have started the switch already):

• E10 (95 octane) – this will replace E5 after 1 September. It will become the standard unleaded petrol. E10 contains up to 10% renewable ethanol, but it's not compatible with 600,000 older vehicles, and while it is unlikely to cost more than standard E5, it's less efficient so you'll probably need to fill up more often.

600,000 older vehicles aren't compatible with new E10 petrol – what are the consequences and how can I check mine?

If you can't use E10, you'll need to use the premium E5 Super petrol which the RAC says costs 146p/litre on average, which is 11p/litre more than other versions.

You can use the free checker on the Gov.uk website to check if your car, van, motorbike or moped is compatible – though note that many manufactures of classic cars aren't listed in the tool, so you may need to contact the manufacturer or retailer directly to ask.

The Government warns the following types of vehicles, in particular, may be incompatible with E10:

• Classic cars

• Some models from the first few years of the millennium

• Many mopeds, particularly those with an engine size of 50cc or under

If I can use E10, by how much will my fuel bills go up by?

The average price per litre of E10 is expected to be the same as it is for E5; currently 135p/litre on average according to the RAC. But the Government says E10 is around 1% less fuel-efficient, which means motorists may have to fill up more often. Based on current RAC prices and typical fuel use, this could add around £18/year to bills.

Is the change coming in across all forecourts?

You'll see E10 in most forecourts in England, Scotland and Wales from September, although there are some exceptions as rural, remote or very small filling stations are able to continue to sell standard E5 where there's limited supply of the alternative E5 Super. In Northern Ireland, the introduction of E10 is expected to take place in early 2022, subject to approval by the UK Government.

What happens if I accidentally fill up with the wrong fuel?

If you fill up with E10 in a non-compatible motor as a one-off, the Government says your vehicle will probably not suffer engine damage, and you won't need to drain the tank.

But it warns that prolonged use of E10 in a non-compatible vehicle could damage it over time. According to the RAC, the extra ethanol can corrode certain metal parts and cause problems with other materials used for seals and gaskets within the fuel system.

My lawnmower runs on unleaded petrol, is that affected?

The Government's warned that some common garden equipment, such as petrol-powered lawnmowers, may also be incompatible with E10. You can't put these details into the Government's tool, so you'll need to check the manual for your equipment or ask the manufacturer or retailer.

When we checked with several major lawnmower manufacturers, John Deere told us all of its equipment going back as far as the 1980s IS compatible with E10, while Hayter told us its latest equipment can also run on the new fuel – though it's unclear if the same is true for its older machinery, so it's best to check.

Are diesel vehicles impacted?

No, nothing is changing with diesel. The Government says diesel already contains up to 7% of a renewable substance called 'biodiesel', which all diesel cars are compatible with.

What more does the Government say?

It estimates that the use of E10 could cut transport CO2 emissions by 750,000 tonnes a year – the equivalent of taking 350,000 cars off the road.