Which has the best interior?

When you travel business class you expect space, comfort and quality – and these cars need to deliver all these attributes by the bucket load.

In the back, the A6 provides the least amount of legroom, and its relatively high-mounted chairs encroach a little on headroom, too. Thanks to their longer wheelbases, the BMW and Mercedes lead the way with rear seats which offer ample space.

However, large transmission tunnels in all three result in the middle passenger having a less comfortable journey than those sitting by the windows. The Audi trails when it comes to passenger space, but it’s the only car here to feature split-folding rear seats as standard. BMW and Mercedes charge £340 and £400 respectively for the helpful set-up. The A6 also has the largest boot, which at 546 litres trumps the E-Class’s by six litres and the BMW’s by 26 litres.

Our three models have a huge array of hi-tech options in the rear to enhance occupants’ comfort – including TVs, window blinds, soft-close doors and heated seats. This means passengers in the back can be treated to the kind of luxuries which used to be the preserve of cars in the class above. There’s an incredible range of technology available up front, as well. Both the 5-Series and E-Class can be fitted with a lane departure system, blind spot warning devices, night vision and adaptive cruise control. The BMW can also be specified with a useful head-up display, while its vastly improved iDrive control system is now far easier to use.

Mercedes’ COMAND set-up offers similar functions, but our SE-spec Audi is the only car here that features satellite navigation as standard. Plus, despite being the elder statesman in this trio, it can still accommodate modern add-ons such as lane departure and blind spot warning. A word of caution, though, because getting carried away with the options can escalate the price alarmingly on all three contenders.

The quality and desirability of the standard cabin are all- important, then, and the 5-Series doesn’t disappoint. With the familiar BMW formula of a minimalist dashboard, classy switchgear and clear instruments, it scores highly for simplicity.

And its materials and build quality are class leading. A huge range of wheel and seat movement makes for a perfect driving position, while visibility is also excellent. In contrast, the upright dash and angular lines of the E-Class cabin mean you don’t feel as cosseted as in the 5-Series. The fact some of the switchgear and materials don’t seem as classy adds to the disappointment. However, the interior is faultlessly put together and we can’t criticise seat comfort.

The A6 immediately feels dated, though. Its driving position is higher set than its rivals’, while the dash layout is cluttered in comparison. There’s nothing wrong with the materials or build quality, but that alone is not enough to win in this category.

BMW: 5 stars The 5-Series’ minimalist cabin features high-class materials and a great finish throughout, while the driving position is perfect and comfort first-rate. The seats have part-electric adjustment, and leather upholstery comes as standard in SE trim. Our car’s oyster-coloured hide is a no-cost option, but the Anthracite wood inlays are £350 extra.

Mercedes: 4 stars There's no faulting Mercedes’ build quality, while cabin space is on a par with the BMW’s. The dashboard isn’t especially stylish though, and it lacks the feelgood factor of the 5-Series. Avantgarde trim includes heated seats, and leather is standard, while the foot-operated parking brake and single-stalk controller are both pure Mercedes.

Audi: 4 stars inside the A6, there’s not quite as much passenger space as in the BMW or Mercedes in this test, while the dash layout is dated. However, it compensates for this with the biggest boot, and is the only car in this test to feature satellite navigation as standard. Plus, we can’t fault its build quality or high-class materials, with leather trim included in the price.