The latest data from BCA for January 2011 shows that average values for petrol models climbed from £4,712 to £5,208, a £316 or 6.7% rise. However, diesel models leapt from £5,883 to £6,654 in the same period; a £771 increase that was equivalent to 13.1% – nearly double the increase enjoyed by petrol cars in relative terms. 

That's despite the fact that the average mileage at sale in January 2011 was 31,265 for petrol fleet & lease volume models and 60,520 for diesel models from this sector.

In terms of CAP performance, diesel routinely outperforms petrol by several percentage points, although there have been bottlenecks where CAP performance has converged over the past two years.

Tony Gannon, BCA communications director, commented: 'There can be little argument that the average price of a diesel car always outperforms that of a similar average petrol model. Research from BCA's Pulse report on high-volume ex-fleet and lease cars shows there is a clear and significant difference in average value at remarketing time – as much as £1,616 in January 2011 – equivalent to a 32.3% variance or nearly a third more on average.'

Commenting on the reasons for the price premium, Mr Gannon said: 'What is certain is that there are a number of factors affecting the relative price performance of the two fuel types in the used car market.  The price paid by motorists at the pumps is significant, and will affect desirability. But motorists don't consider this in isolation – our research for the Used Car Market Report shows that they also value diesel's perceived relative economy in terms of mpg and lower servicing costs.'