Sector: Executive Price: £34,365 Fuel: 64.2mpg CO2: 114g/km

Carmakers have achieved some miraculous feats with the diesel engine in recent years and, while hybrid and petrol technology is beginning to show its strengths in the fleet sector, Audi’s most fuel-efficient A6 to date is a reminder of why the market still favours this fuel.

Think of the ‘ultra’ brand as Audi’s equivalent to BMW’s EfficientDynamics technology. It stands for the brand’s most fuel-efficient vehicles, but with gains in frugality achieved through subtle or invisible tweaks, rather than blunting performance or luxury, and adds up to some appealingly low running costs for corporate users.

At the heart of it all is a new Euro 6 compliant 2.0-litre TDI engine, which now produces 188bhp instead of the old version’s 175bhp, and a seven-speed S tronic dual-clutch gearbox instead of the stepped Multitronic CVT used in the past. Hardly short of power, it’ll reach 62mph in 8.2 seconds and peak torque is available across the most commonly used part of the rev range, giving strong in-gear acceleration.

In real-world terms, this means the A6 ultra can trickle along at higher speeds, in seventh gear, just outside its peak power band and barely use any fuel. Audi claims fuel economy of 64.2mpg for all trim levels, and in S line spec it easily returned almost 60mpg on the motorway. But without idiotically high gearing, the power is accessible with a nudge of the throttle.

To put that into perspective, the old A6 2.0 TDI Multitronic returned 56.5mpg and emitted 132g/km of CO2. Though that’s far from unimpressive for a car of this size, its replacement makes those figures look decidedly lacklustre.

Yet Audi has chosen not to shout too loudly about its frugality. There’s a tiny ‘ultra’ badge on the boot lid, but no aerodynamic bodykit or tiny aerodynamic wheels to reduce drag and rolling resistance. On the contrary – this drivetrain can be paired with the A6’s usual SE, S line and Black Edition trim levels, with wheels of up to 20 inches in diameter, without hurting fuel economy or CO2 emissions.

So for what is ostensibly an eco-friendly car, the A6 in S line spec features a full leather interior, infotainment system with satellite navigation and a 6.5-inch screen, keyless entry and parking sensors among its list of standard equipment. As with all Audis, it’s possible to get carried away with the options list, but this really offers all of the equipment a travelling executive could need, and all in a sublimely comfortable long-distance car.

Best of all, it’s not expensive. There’s no shortage of fuel-efficient rivals but, in the S line trim that’s so popular with UK customers, the A6 is the most fuel efficient and the cheapest too, by just over £2,500. However, official figures aside, filling the saloon’s wheel arches is likely to shorten the distance between fuel stops in real-world driving. 

So while diesel is starting to come under political pressure, cars like this serve as a good reminder of why it's become so popular in the corporate market. The A6 ultra does everything a far-travelling executive could need, including reducing the time spent on forecourts filling up, and asks nothing in return. 

Verdict:

With low running costs and no sacrifices for the end user, the A6 ultra means even executive-level employees can contribute to carbon reductions without giving up creature comforts.