Glass's AutoProvision forecasting tool predicts a 44% fall in first year values for Honda's petrol-electric Insight, with 12-month old 12,000-mile examples expected to sell at just £9,500 – considerably less than its £17,000 list price.
Honda has begun offering low-mileage used Insights, which are three-door coupes only, on its UK website with prices starting at less than £10,000.
Values for the £16,000 Toyota Prius – a four-door saloon petrol-electric hybrid – have fallen more sharply, according to Glass's, with one-year-old cars retailing at £8,400 after racking up 12,000 miles.
Steve Crawshaw, Glass's forecasting editor, said: 'Only those buyers who have done their homework are fully aware of the grants that are available for these cars and this means many prospective buyers are put off by the high list price.
'While nobody should have paid full price for these cars after Government grants are taken into account, the hybrids are nevertheless suffering unusually high levels of depreciation.
'There are concerns about potential repair bills for such innovative technology and with modern diesel engines returning comparable levels of fuel efficiency, it is clear that buyers need to be particularly conscious of the environmental impact of emissions to make the investment.'
Robert Hester, editor of CAP Black Book, said: 'I haven't seen any Priuses come through auctions yet, and I image that many of them would be run by Toyota and kept within the company.
'I have seen one or two Insights at auction and they seem to stay within the Honda dealer network. These are then put on sale for £9,995 which means dealers are probably paying £7,000-£7,500 which would reflect the CAP Monitor figure of £6,825 on 12 months/10,000 miles.
'The Honda is only a two-seater which limits its appeal and they are not the prettiest cars in the world. The British public is just sceptical about new technology such as petrol-electric hybrids, and I think these cars will continue to struggle.'