Auto Trader said the difference was down to a surge of EVs previously bought on finance or leasing contracts re-entering the market.
This has led to the supply of middle-aged EVs jumping by 108pc since the start of the year, although demand has increased by 152pc as well.
The strong second-hand figures come against a backdrop of lacklustre demand in the new car market, with the SMMT this week lowering its forecast for new EV sales in 2024.
Mike Hawes, chief executive of the SMMT, said: “The increased supply of electric vehicles to second and third owners is helping more motorists make the switch – underlining the importance of energising the new EV market to support a fair transition for all.
“Maintaining momentum requires reliable, affordable and green EV charging up and down the country and incentives to get all of Britain on board the net zero transition.”
Used cars represent the vast majority of the UK’s passenger car market, with roughly four in five of all sales involving a second-hand vehicle.
Overall the SMMT said there were 1,963,395 used car sales in the second quarter of 2024, an increase of 7.2pc year-on-year.
Separately on Wednesday, Sixt, Europe’s biggest rental car provider, said it was cutting the number of electric cars it would hold because customers preferred combustion engine vehicles.
In a statement, the company said: “We direct our share of EVs according to consumer demand and can very quickly react to demand changes.”
Last year, Sixt had 170,000 vehicles of which just under 10,000 were electric.