Electric vehicle (EV) residual value (RV) forecasts for the UK are moving closer to traditional diesel cars as the used car market becomes more accustomed to the technology they contain, according to valuation company Glass's.

In some cases, EV RV forecasts for are already broadly similar to their diesel equivalent, according to Glass's head of valuations, Rupert Pontin.

He said: "The residual value gold standard for EVs is the Tesla Model S. Its minimum 220 mile range means that its three year/60,000 mile value is around 43% - almost exactly the same as a well-established direct competitor, the BMW M535d M Sport."

Elsewhere in the market, EV values are also closing the gap on diesels. The Vauxhall [Opel] Ampera Electron's 27.58% at three year 60,000 miles value is not far adrift of the Insignia SRI CDTi diesel's 34.56% while the BMW i3 range extender (REX) in Suite trim at 39.11% is just a few points away from the BMW 320d Sport's 43.46%.

"Clearly, there is still a difference here between EVs and diesels but there are signs that it is closing all the time. Crucially, when the overall running costs of an EV are taken into account, factors such as savings on fuel mean that they may beat traditional models."

A major boost in the last few months, Pontin added, was Nissan's announcement a new battery pack for its Leaf EV would cost EUR5,000 (GBP3,560).

He said: "RVs of the Leaf are among the poorest of the EVs at around 29% at three years/60,000 miles because there are quite a number around.

SMMT data shows Nissan UK sold 4,051 Leafs in 2014, up 124% year on year. To the end of February, the YTD tally was up 67.9% to 450.

Glass's Pontin said removing the mystery surrounding the battery pack pricing took away a large degree of uncertainty from forecasting the Leaf's RVs.

"While [GBP3,560] is expensive, it is something that can be planned into a budget when you are making an RV forecast."

Pontin said it was likely EVs' RVs would "continue to close the gap on diesels as used car retailers and buyers became more familiar with the technology. Critically, the battery power improving will mean a better real world driving range".

He added: "EVs of one kind or another currently account for about 2% of the market. However, if the UK is to meet its 2020 emissions target of 95g/km per vehicle, their penetration must increase quite rapidly. As this happens and they become a more familiar part of our daily lives, we expect EV RVs to firm up and stabilise."