Audi has dominated the large, premium estate car market for years with the A6 Avant, and the company has high hopes for this fourth-generation car which offers more interior space, greater economy and better performance than the model it replaces.

All the A6s have a steel/aluminium body. The main structure is a fairly conventional steel monocoque, but the front suspension turrets are cast aluminium, as are several other components under the skin and 20% of the exterior panelwork. As a result, Audi says the A6 is up to 20% lighter than a convential steel car of the same size - which gives the big estate class-leading performance, economy and CO2 figures.

Quattro four-wheel drive and S-tronic dual-clutch gearbox make the most of 3.0TDI's 245PS, but low-profile tyres generate plenty of road noise.

The biggest seller in the new range is the 177PS 2.0-litre turbodiesel engine, mated to a six-speed manual gearbox and front-wheel drive. A Multitronic CVT is optional. There's a 3.0-litre V6 turbodiesel with 200PS and the Multitronic transmission, and a 245PS version with quattro four-wheel drive and the S-tronic dual-clutch gearbox. Petrol engines are increasingly rare, but you can get a 300PS 3.0-litre TFSI V6 with quattro and S-tronic. A bi-turbo 313PS TDI is due for launch in February 2012.

All the A6s impress with a tidy, tastefully-trimmed cabin which offers leather and satnav as standard. The diesel engines are quiet and smooth, with performance ranging from acceptable (in the 2.0-litre) to distinctly rapid (in the more powerful of the two 3.0s), while the 3.0-litre TFSI is faster still but pays an inevitable fuel consumption penalty. The Multitronic CVT auto suits the V6 turbodiesel well, making for swift and unobtrusive progress, and the S-tronic dual-clutch transmission has fast, smooth gearchanges.

Biggest-selling A6 Avant will be this 2.0TDI version, which is quicker and more economical than the car it replaces. Interiors are impressive, leather standard.

There are few demerits, but they're significant ones: in the manual cars the clutch is long of travel with indistinct bite, the variable power assistance for the steering feels more like an intermittent fault than a driver assistance feature and road noise dominates the soundscape in all the A6 Avants - particularly if you spend £2500 on the optional 20in alloy wheels wrapped in slivers of 35-series rubber. If comfort and refinement are a priority, you would be better off keeping the standard 17in wheels and spending the money on air suspension, another entry on the extensive options list.

Those niggles apart, the A6 is a worthy opponent for premium estates from BMW and Mercedes-Benz, and it won't be long before it's a best-seller.