Hostilities are expected to push up the price of fuel, with prices already rising rapidly, and the firm says that more buyers will reject those vehicles perceived to be 'gas guzzlers'.
Jeff Paterson, senior car editor at Glass's, said: 'We can expect to see an acceleration of several established trends such as falling sales for large petrol off-roaders and non-diesel powered executive cars and the growth of fuel-efficient small and medium cars, especially those powered by diesel engines.
'Wider awareness of the refinement and economic benefits of modern diesels will ripple down even faster to the secondhand market, preventing any significant drop in values over the next few years, despite the marked increase in supply.'
The firm admitted that UK involvement in an invasion of Iraq would deter used car buyers from spending money, but it would only be a short-term effect. Paterson added: 'This lull in sales activity is unlikely to extend beyond a month or two.'