The price of new battery electric cars has fallen below petrol cars in the UK for the first time, according to the car sales website Autotrader, in a significant milestone in Britain’s transition away from fossil fuels.

The average price of a new electric car listed on the website was £42,620, compared with £43,405 for a new petrol model – making the former £785 cheaper based on advertised prices after discounts.

The higher upfront cost of electric vehicles has long been one of the big sticking points preventing some drivers from switching away from cars with polluting petrol and diesel engines towards those with battery motors, which do not emit carbon dioxide directly. Total running costs for electric cars have been lower for some time.

UK battery electric car sales accounted for 22% of new car sales in the first three months of the year, according to the Society of Motor Manufacturers and Traders, a lobby group.

Prices in the UK have been pushed down by the electric car grant brought in last summer, offering up to £3,750 off some models. Carmakers have also been under intense pressure to drop prices to meet electric car targets, known as the zero emission vehicle (ZEV) mandate, and from an influx of Chinese competitors that have been able to undercut traditional brands.

Autotrader is the UK’s biggest automotive marketplace, although it does not cover all transactions across the country. The data suggests that the UK has reached a pivotal moment for decarbonising its road transport, as a cheaper upfront cost and significantly lower running costs combine to make electric cars increasingly attractive to buyers.

Bex Kennett, the head of new car at Autotrader, said: “The electric car market is becoming increasingly competitive, and despite the challenges created by the ZEV mandate, manufacturers and retailers have worked hard to improve both the supply and affordability of new electric vehicles.”

Kennett said carmakers had been forced into “historically high levels of discounting earlier this year” as they tried to increase electric sales. However, their efforts appear to have been aided by the war in Iran, which has caused a rise in petrol and diesel prices. Car sales platforms across Europe have reported large increases in inquiries for electric cars from consumers keen to cut their energy costs.

Gurjeet Grewal, the chief executive of Octopus Electric Vehicles, the car division of the energy company, said the term milestone “gets thrown around a lot, but this really is one. For the first time, EVs are cheaper than petrol cars on upfront cost – removing one of the biggest barriers to switching.

“They’ve long been cheaper to run, and now they’re cheaper to buy, too. Add in growing competition and more choice, and it’s clear the direction of travel: electric is the obvious option for drivers.”

However, the transition to electric cars in the UK still faces some barriers. Households across the country who do not have driveways are reliant on the public charging network, which remains patchy in some areas.