Research by CAP Black Book experts shows diesel prices generally improving while the trend for petrol cars is going the other way. For instance, although a Rover 214 SLi has dropped £200 between January and April, the diesel version - the 218 SLD - has held steady.

However, that view was disputed at this week's British Vehicle Rental and Leasing Association-organised residual value seminar where Richard Lownsborough, who heads up Reg Vardy's used car buying division, claimed the diesel premium had disappeared.

Meanwhile anti-diesel stories have surfaced again with Fleet News (April 19) reporting a Mobil survey which warned that 50% of diesel vehicles could fail emission tests. But stabilising diesel prices have come too late for some. As the recession lifts, there has been a swing back to petrol. Secondhand buyers keen to avoid risks have reacted to every piece of news on emissions by interpreting the stories as a potential threat to their purchasing decisions.