DIESEL executives have traditionally been unfavoured in a sector where the emphasis is more firmly based on refinement and performance. Needless to say most sales volume in the class has come from 'quality' manufacturers such as BMW, Mercedes-Benz and Audi, where image has made up for any stigma that might be attached to diesel.

But as technology improves, the economy advantages of diesel are becoming too great to ignore, particularly with impending budgetary tax changes that are anticipated to affect more expensive prestige cars. And with a new 2-litre direct injection diesel from BMW debuting in the new 3-series this autumn, competition is hotting up.

The advent of Audi's all-new 150bhp 2.5-litre direct injection V6 turbodiesel, now on sale priced from ú26,320 and shortly to be road tested in Fleet News, gives the company a second diesel option in the A6 range: the established 1.9-litre four-cylinder direct injection engine developing 110bhp we test here is a unit that's been around in Volkswagen and Audi products for some time, but it marks the entry to the A6 range with an on-the-road price of ú22,570 for the standard model and ú24,535 for the better-equipped SE.

In comparison with its immediate 'quality' competitors from BMW, Mercedes and Volvo, it has only four cylinders and less power than the 525tds (143bhp), C250 TD (150bhp) and S70 TDi (140bhp). But at its price, it is also substantially cheaper than the competition, undercutting the least expensive rival - the Mercedes - by almost ú2500. As only the C-class range offers more than one diesel engine option - the normally-aspirated 95bhp C220D - it's an undoubted opportunity for Audi in the sector.