Audi has been turning out some racy-looking machines like the R8 and TTS of late. This is not one of them – but don’t underestimate the S6 quattro merely because it does not look flash.

It may go about its business in an unobtrusive manner but it’s nevertheless a quick car, capable of hitting 60mph in around five seconds.

As the sporting flagship of the A6 range, the S6 tends towards the understated and conservative.

Exterior styling differences are of the subtle variety, the interior is not hugely dramatic and even the engine note is relatively muted – despite its effortless performance.

Only the winking LEDs lights at the front are perhaps out of character and contrive to give the game away. For under the bonnet of the S6 is a hulking ten-cylinder, five-litre Lamborghini engine, which pushes out 430hp and requires not one but two electronic management systems.

That’s a fair amount of grunt and the S6, despite its weight of nearly two tonnes, is particularly rapid off the mark, so care needs to be taken with the throttle.

With four-wheel drive to keep you secure in the wet and Audi’s six-speed Tiptronic auto gearbox taking the strain off your left arm, the S6 is perhaps not the most involving of drives.

But it is hugely competent and stable on the road, with vast amounts of grip from its 265/35 R19 tyres.

Refinement is good – perhaps too good for a sports car – though the engine does start to ‘sing’ when pushed. The ride is firm though not in teeth-jarring territory.

The cabin will be familiar to any Audi owner. It’s beautifully built and straight forward to operate. Everything feels impressively solid and functional.

The S6 is also very practical for a sports-focused car. It seats five with ease and has a large boot with a capacity of nearly 550 litres.

There were one or two things on the option list which arguably should be standard on a car costing over £50,000 – like mobile phone connectivity, DAB and an electrically-adjusting steering column.

But most buyers will probably be more concerned about the power plant rather than seeking the last word in luxury.

Service intervals can stretch to nearly 20,000 miles but do not expect running costs to be cheap. Insurance and tax will be dear and you’ll be lucky to get 20mpg. Nor are residuals likely to be among the highest.

The S6 is not as sexy as the new Jag XF, nor as quick as the BMW M5 – though neither is it as complicated to operate. It’s capable, yet discreet, practical and easy to live with.

And did I mention the Lambo under the bonnet?

By Peter Carroll