Drivers of older cars must continue to use E5 petrol to avoid the risk of damage.
The Historic & Classic Vehicles Alliance (HCVA) says classic cars will "run more efficiently" when topped up with higher octane petrol.
Now E5 will continue to be sold at most forecourts even after the changes, but it's likely to be harder to find the fuel.
Under the Super Unleaded grade it means it'll be slightly more expensive than what it was at the start of this month.
However, a spokesperson for HCVA said the cost premium is "not huge" especially if drivers shop around.
Malcolm Mckay said: "Fuels with lower ethanol content (labelled E5) are still available.
"The government pledged to keep it available for five years and this dispensation is renewable, but availability depends on demand."
He added: "The only E5 fuels available are the higher octane ones – 97 or 99 octane – but this is not a problem as all petrol vehicles will run on them and, if properly adjusted, will run more efficiently on these fuels, counteracting to some extent their higher cost.
"If you shop around, the cost premium is not huge – most supermarkets stock 97 octane E5, though sometimes only at one pump.
"For older engines with 9:1 compression or higher, that were originally designed for 100 octane fuel, 99 octane fuels are available."
The HCVA says older models requiring 99 octane fuel should look at high-street fuels such as Esso's Synergy Supreme+ 99.
They also recommended Shell V-Power 99 which contains no more than 5% ethanol.
Esso confirmed to the HCVA its 99 octane fuel is ethanol-free in the majority of UK forecourts.
Classic car owners are urged to not use the new E10 fuel due to the possible risks involved with the new fuel.
Experts at Hagerty claim tests from the Department for Transport (DfT) identified a range of issues.
Millions of drivers admit they're embarrassed of their cars – from brand to age
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These included degradation of fuel hoses and seals, blocked fuel filters and damaged fuel pumps.
They also identified corroded carburettors, blocked injectors and corrosion of the fuel tanks.
The RAC has previously said around 600,000 cars will not be compatible with the new petrol.
Cars built before 2002 are impacted, but E10 compatibility was only required of new models from 2011.
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