When What Car? magazine conducted a series of tests of E10 bioethanol fuel against pure petrol, it found a reduction in fuel economy ranging from six to 11.5 per cent, with larger-engined cars suffering the least.

Because of the increased fuel consumption, CO2 emissions also rise, although that increase should be partly compensated by the renewable aspect of the bioethanol, as it’s distilled from plant material. The most common sources are corn or sugar cane, although cellulosic ethanol distilled from plant and wood fibre (cellulose) is seen as a more environmental alternative.

Can you use superunleaded instead?

Yes, but it will be even more expensive than the regular E10 petrol. Despite remaining E5 it has a higher octane rating of 97-plus to justify the “super” tag – essentially meaning it’s more combustible and therefore more efficient. Superunleaded petrol also tends to contain more detergents and performance enhancers than the regular grade of unleaded, which adds significantly to the extra cost compared with E10.

When E10 became the regular grade of petrol last year, fuel prices were already at their highest for eight years. The RAC’s fuel spokesman Simon Williams said at the time: “Those drivers who have no choice but to use superunleaded E5 petrol will be paying through the nose.

“This will quickly mount up for anyone who has to drive a lot of miles to get to work every week. It’s also probably the case that many of those driving older cars will be from lower income backgrounds, so they will end up being even worse off.”

What about diesel?

Diesel prices are consistently higher than those for petrol, although you’ll get greater economy from a diesel than from a petrol engine. However, the fuel has been demonised for nitrogen dioxide and particulate emissions and sales have declined drastically.

The ratio of bioethanol in diesel is unchanged at up to seven per cent.