IT may be the final frontier for Captain Kirk and Dr Spock - but for buyers of estate cars space is also very much a prime consideration.

Often, though, the extra load lugging capacity offered by these family wagons means we are forced to sacrifice some performance.

But that need not be the case if you've got £40,000 burning a hole in your pocket - because this 3.0-litre diesel version of Audi's A4 Avant is a roomy estate that refuses to compromise.

Available only in range-topping S line trim and with the German car maker's acclaimed quattro all-wheel drive system this is the flagship model of this year's rejuvenated A4 Avant range - and it packs a real punch.

The V6 powertrain is paired exclusively with a versatile and super-smooth eight-speed automatic gearbox and delivers sports car pace and acceleration, capable of 0-62mph in just 5.4 seconds and an electronically limited top speed of 155mph.

The lowered S line suspension, which has been totally re-engineered, along with well-weighted, responsive power steering and the assured grip of the quattro system also make for some dynamic handling. This is an estate that you can drive enthusiastically with total confidence.

Motorway miles are eaten up with ease while the car remains composed and well-balanced taking on winding A-roads and proves equally relaxed and refined even in stop-start urban traffic.

Audi's five-mode drive select system is standard across the range and if I were really nitpicking, then there's a split second's delay in throttle response when in ‘comfort' or ‘efficiency' modes.

Flick it into ‘dynamic' mode, though, and this issue disappears as a sharp thrust on the gas pedal see's you gently forced back into your seat as the car takes off sharply.

As well as offering power, poise and pace, though, the A4 Avant is at the front of the space race too - the new model's 505 litre boot being 15 litres bigger than its predecessor's and topping those in both of its premium German rivals - the Mercedes C-Class estate and BMW 3 Series Touring.

Load capacity rises to 1,510 litres with the rear seats, which are split 40:20:40 for extra versatility, folded flat. A low load lip makes lifting heavy items on board easy while all A4 Avants get a powered tailgate.

The cabin space is as classy and well-appointed as we have come to expect from Audi with solidly assembled, high-quality materials all around and plenty of storage options for personal items, while head and legroom is good all round.

Equipment levels are generous across the range and this flagship gets a seven-inch multimedia touchscreen interface with mobile phone mirroring capability, climate control, satnav, DAB radio, Bluetooth, automatic lights and wipers and keyless entry and ignition.

Typically of Audi, though, there is also a long options list and niceties such as an upgraded Bang & Olufsen stereo, heated seats, head-up display, parking assist, panoramic sunroof and adaptive suspension all helped to add a whopping £12,000 or so to the price of this model.

For that outlay you'll want to keep running costs down so it's good to see that even this performance-focused flagship posts a potential 53.3 miles per gallon on average with carbon emissions of 139g/km.

These figures do change to 52.3mpg and 142g/km with the optional 19-inch alloys my car had - but that's not bad for such a powerful car and is the reward for Audi's efforts to make the new model lighter and more aerodynamic.

Company buyers might well be more tempted by 2.0-litre diesels which offer up to 70.6mpg and emissions as low as 104g/km while there are also 2.0-litre and a new 1.4-litre petrol options too.