IF this is the second diesel A6 we've tested in the last few weeks, we make no apologies. Things are moving quickly at Audi, and with the company's technological advantage over most rivals with its use of direct injection, there's good reason to shout about economy. But with a new 2.5-litre V6 direct injection turbodiesel

developing 150bhp supplementing the existing four-cylinder 110bhp 1.9 TDI, Audi is adding refinement into the equation while keeping a wary eye on economy.

Diesel fuel in the UK is among the most expensive in the EU, matching petrol virtually penny for penny pricewise, and while the Spring Budget may not have done diesel-engined cars many favours, it has incentivised the use of low-sulphur fuel by pegging the price rise per litre to 4.4p - identical to the rise for unleaded - compared with 5.5p for regular diesel. So with clean-burning, efficient direct injection combined with low-sulphur diesel fuel, an oxidising catalytic convertor and exhaust gas recirculation this engine promises to be one of the cleanest around as well as one of the most powerful. Question is, at ú28,284 on the road for the SE (or ú26,320 for the less well-equipped standard model) is the V6 TDI worth almost ú3750 more than the 1.9 TDI 110?