Audi responds to questions about whether it is over-burdening customers with too much choice by pointing out the demand, and it's hard to argue against. Over the first eight months of the year they've sold 57,268 cars, out-stripping rival BMW's 54,703.

Get behind the wheel of an A5 Sportback and you can't miss the reasons for Audi's continued success.

The interior is up to Audi's typically excellent standards of form and function. Take the steering wheel as an example: it's thickened where your fingers grip it, is well-weighted, has a couple of switches for audio controls and a mini-grille mimicking the car's nose.

Diesel engines impress

The quiet, smooth diesel engines seem to suit the car best, with ample grunt and a thoroughly refined manner. Audi expects most buyers (the majority of which will be on company car schemes) to plump for an oil-burner.

The 3-litre diesel, with optional S tronic gearbox, pulls the car to 62mph from a standstill in 6.1 seconds (the manual takes 0.2s longer) and reaches 155mph. Yet it returns 42.8mpg on the combined cycle and emits 174g/km of CO2.

The 2-litre diesel offers the best fuel economy, but is only available with a manual gearbox. It emits 137g/km of CO2 and gets 54.3mpg. But the 0-62mph time falls to 8.7 seconds and the top speed is 141mph.

What's more, the same engines are available in other models - so what sets the A5 Sportback apart from its Audi brethren?

Its low roofline and frameless doors fulfils the 'sport' in Sportback. But there's no getting away from the compromises the four-door form have imposed upon the muscular looks of the A5, and the end result is rather too reminiscent of the A4 and A6.

Although it's wider than an A4, the Sportback is a four-seater. With all the seats in place it has the same 480 litre capacity as the A4 saloon - when folded flat it offers 980 litres to the A4's 962.

A niche of its own

Audi is right when it points out that the A5 Sportback is in a niche of its own, it's just a rather small one. And it's hard to make a case for the cosmetic difference being worth the £3,220 premium over an A4 (comparing base models).

But Audi has the golden touch and it confidently predicts strong residual values for the A5 Sportback - it believes the 2.0 TDI will hold 43 per cent of its value after three years.

The A5 Sportback is another wholly accomplished product and it's likely to be another sales success for Audi.

View a video review of the Audi A5 3.0TDI Quattro from New Car Net: