E10 petrol and classic cars: what the government actually says, and what the clubs add

Petrol changed on 1 September 2021, and for most drivers nothing happened. The standard 95-octane grade became E10, containing up to ten per cent ethanol, every modern car carried on as before, and the circular E10 labels on the pumps became part of the furniture.

For owners of older cars it was a different event, and one surrounded by more confident misinformation than almost any other topic in classic ownership. Here is what the government’s own documents say, what the historic vehicle federation adds, and what is and is not guaranteed about the alternative.

What changed, precisely

The regulations that took effect in Great Britain on 1 September 2021 set a minimum ethanol content of 5.5 per cent by volume for the standard 95-octane grade, which in practice means the E10 blend allowing up to ten per cent. Northern Ireland followed in November 2022.

The mechanism matters for one reason: the law did not mandate ten per cent, it mandated at least five and a half, so the exact ethanol content of a given tank of E10 can vary within that range. What it cannot be is E5.

The government’s own wording on older cars

The official guidance on E10 is more careful than the forum summaries of it. It states that all new cars manufactured since 2011 are compatible with E10. It then lists the vehicles that may not be compatible: classic, cherished and older vehicles; some specific models, particularly from the early 2000s; and some mopeds under 50cc.

Note the hedge. The guidance does not say classics cannot use E10. It says they may not be compatible, and it leaves the question to the manufacturer.

The Department for Transport was blunter in the consultation that preceded the change. It stated that it is not straightforward to set out which vehicles produced before 2011 are approved for E10 use, as there are no clear cut-off dates, and that compatibility needs to be confirmed by manufacturers for each model. It went further on one marque, noting that cars from manufacturers like Rover, which had ceased trading and could not provide compatibility information, were therefore not recommended to use E10.

That is the honest position for every classic whose maker is gone: the only body that could certify compatibility no longer exists, so compatibility cannot be certified. The government’s own compatibility checker, built from data supplied by the European manufacturers’ associations, carries the same limitation, and it states plainly that fitted replacement parts affect its accuracy, which on a fifty-year-old car means nearly everything.

The practical consequence is the one the Federation of British Historic Vehicle Clubs draws: vehicles produced before 2000 should use the E5 protection grade, where ethanol is limited to five per cent. Some super grades contain no ethanol at all, though availability varies by brand and region.

A tank of E10 is not a catastrophe

Worth stating clearly, because the alarm on this point is disproportionate. The government guidance says that using a single tank of E10 in a vehicle that is not compatible should not be a major problem, and that it is prolonged use that may cause harm and is not recommended.

Ethanol’s effects are cumulative. One fill of E10 on a journey where nothing else was available is a non-event; run the car on it for a year and the rubber and the tank will tell you. Mixing the two grades in a compatible car is, in the government’s words, perfectly safe.

What ethanol actually does

The government’s explanation is narrow and worth quoting: higher blends of ethanol can cause corrosion of some rubbers and alloys used in the engines and fuel systems of some older vehicles. Its documents say nothing about water absorption or storage; those mechanisms come from the federation, and they are the ones that matter most to a car that sits.

The FBHVC identifies three effects.

Corrosion. Ethanol has increased acidity, conductivity and chloride content compared with conventional petrol, which can corrode and tarnish metal components: brass, zinc alloys, aluminium, and the steel of a fuel tank.

Perishing. Elastomer materials, meaning the rubber of fuel hoses, seals, diaphragms and carburettor components, swell and soften in contact with ethanol, weakening their structure, and then shrink and crack on drying out. A fuel line that has done this is a fire waiting for a reason.

Water. Ethanol absorbs moisture from the air. In a car in regular use the water passes through with the fuel. In a car that stands for months with half a tank of E10, the water collects, the fuel can separate, and the tank corrodes from the inside. This is the mechanism behind the federation’s advice that a car to be laid up for an extended period should be stored with the right fuel in it, which is covered in our guide to laying up a classic for winter.

E5 super: available, but read the guarantee

The reason E5 is still on the forecourt is not market demand. It is law.

When E10 became standard, the regulations required that the 97-plus octane super grade contain no more than five per cent ethanol, as a protection grade, at filling stations that sold over a million litres of fuel in the previous calendar year and stock at least two grades of petrol. The government’s guidance says E5 will remain available at filling stations that sell two grades of petrol.

Two limits on that guarantee deserve attention.

Small stations are exempt. Very small filling stations, selling under a million litres a year, and those in the rural fuel duty relief areas are not required to stock the protection grade. That is why a country forecourt may sell E10 only, and why a classic touring in rural Scotland or the West Country is wise to fill up before the towns run out.

The requirement was set for a minimum of five years, with a review. The protection grade was legislated to last at least five years from September 2021, which is the longest period a regulation of this kind can run before it must be reviewed, and the consultation noted that it could be extended subject to that review. Five years from September 2021 is September 2026. As this page is written, the future of the protection grade beyond that review is a live question rather than a settled one, and anyone whose car depends on E5 should check the current position on gov.uk rather than assume the forecourt will look the same next year.

Additives: what the federation now says

For years the FBHVC endorsed named fuel additives, and the endorsement appeared on bottles. It no longer does. The federation ceased endorsing aftermarket fuel additives because keeping up with changing formulations and performance claims, and testing each in historic vehicles, became impractical. No product names appear on its current guidance.

Its position on the category is precise and worth keeping precise. Corrosion inhibitor additives can be very effective in controlling ethanol-derived corrosion, and the federation recommends them as an additional precaution. But it is not aware of any additive that claims complete fuel system protection for elastomer and gasket materials.

So an additive addresses one of the three problems. It does not stop hoses perishing, and it does not stop water accumulating in a stored tank. The defence against those is mechanical: ethanol-resistant fuel lines and seals, which are cheap and available for most classics, and sensible storage.

The practical summary

For a car built before 2000, use E5 super where you can get it, fill up before rural areas, and do not panic about the occasional tank of E10. Replace fuel hoses and seals with ethanol-resistant modern equivalents, which solves the perishing problem permanently and is the single most useful change. Add a corrosion inhibitor if you wish, knowing what it does and does not cover. And store the car with the fuel question settled, either drained or brimmed and stabilised, rather than left to chance.

The one thing to keep an eye on is the protection grade itself. The law that keeps E5 on the forecourt came up for review in September 2026, and the answer to that review will matter to every classic that cannot be certified for anything else. Check it before you plan on it.