It was raining. The road was smooth, shiny and slippery – perfect conditions for testing this new diesel Audi TT TDI quattro, a car that is claimed to be the world’s first diesel-powered sports car. Or so I thought. Accelerating gently through a long curving bend, the all-wheel-drive Audi felt no less secure than had the road been dry.

Suddenly a queue of cars appeared in front, and my chum, who was driving, lifted his foot off the accelerator. In that instant the TT tried to throw us off the road. Thanks to the skill of both the driver and the TT’s electronic stability system, an embarrassing and expensive encounter with the scenery was fractionally avoided.

I mention this only as a warning to those who consider a four-wheel-drive car to be somehow safer. It’s not: it encourages people to drive hard in bad weather and it can create a false sense of security and therefore raise the speed at which you’re travelling before you realise the danger you’re in. And the moment you spot that danger and lift your foot from the throttle, you have no-wheel drive, like every other car on the road.

In theory this TT would be much improved by using the standard front-wheel-drive hardware offered by the entry-level models because the result would be cheaper, lighter, more frugal and environmentally friendly. In practice, however, directing the considerable torque of its 170bhp diesel engine through the front wheels alone would almost certainly start to interfere with the way the car steered, so four-wheel drive it is.

Even so, none of this stops the TT diesel being the most convincing since the breed’s inception 10 years ago. Indeed, Audi has worked something close to a miracle to persuade a 2 litre four-cylinder diesel motor to perform as well in the context of a sporting coupé as this one does in the TT. It sounds like no other diesel I’ve encountered, producing a convincing and attractive throaty growl at medium revs; and while other diesels become breathless at about 4000rpm, this one keeps going past 5000rpm, if you so choose. Yet if you treat it as you would any other diesel and keep the revs low and the gears high, it still offers all the effortless thrust you’d expect.

To put this into perspective: as well as introducing me to the diesel TT, Audi let me drive the most sporting TT yet, the 272bhp TTS, and despite boasting an extra 100bhp over its diesel stablemate, it has not the smallest sliver of extra torque. When you put your foot down at, say, 2000rpm the two cars react in much the same way. It’s only when you make the TTS engine rev to speeds the diesel motor won’t reach that its extra pace is evident. And what TT driver is likely to do that on a regular basis?

This is a significant point: the TT may be faintly sporting in character but despite Audi’s protestations, a sports car it ain’t, whether it be powered by diesel, petrol or anything else. The reason Porsche won’t be putting diesel into any of its engines any time soon is that it knows that diesel is an entirely inappropriate power source for proper sports cars. Instead the TT is now what it was when launched 10 years ago: a beautifully built mobile fashion statement that nobody placing driving dynamics at the top of their priority list would look at twice.

There is nothing wrong with this, and the fact that the TT diesel delivers all the performance most potential customers will want or need, and requires even less effort, is a point in its favour. So, too, is the fact that it should do more than 50mpg on a gentle run and, with emissions of 139g/km, it will go easy on company drivers with a tax bill to pay and private owners with a licence to buy.

I found the TT surprisingly well suited to diesel power. True, Audi’s claim that the TT diesel is “the first series production sports car in the world to be powered by a diesel engine” stands not a moment’s scrutiny – despite pricing the TDI at an identical £26,350, it appears to have forgotten that the quicker, more powerful and sporting BMW 123d M Sport coupé hit the market some months ago. However, you can’t mark down a car for the marketing guff. Or at least I can’t.

Vital statistics

Model Audi TT TDI quattro
Engine type 1997cc, four cylinders
Power / Torque 170bhp @ 4200rpm / 258 lb ft @ 1750rpm
Transmission Six-speed manual
Fuel / CO2 53.3mpg (combined cycle) / 139g/km
Performance 0-62mph: 7.5sec / Top speed: 140mph
Road tax band C (£120 for 12 months)
Price £26,350
Verdict The TT and diesel make an odd couple but a good marriage
Date of release Summer

The opposition

Model BMW 123d M Sport £26,350
For Great blend of power, economy and emissions
Against Cramped rear seats, ugly from some angles

Model Alfa Romeo Brera 2.4 JTDM £26,995
For Beautiful inside and out, smooth, powerful engine
Against Not great to drive, lacks German build quality