The Mini EV electric costs just over £1,800 over the years, while the Mini One petrol car will set drivers back almost £4,500.
Lisa Barber, Which? Home Products and Service Editor said affordability of electric cars was a “significant barrier” to more adoption.
She said: “Millions of people are expected to switch to electric cars over the next few years to reduce emissions, however our research shows that affordability is a significant barrier and the upfront cost of purchasing an electric vehicle is putting people off.
“We know consumers want to make more sustainable choices and are open to switching to electric vehicles.