Auto Start-Stop isn’t the only bit of gear in the Cooper D’s bag of tricks, though. MINI has imported a slew of economy-boosting technology from its parent company BMW, launching them under the ‘Minimalism’ (geddit?) moniker. It’s essentially the same tech developed under BMW’s EfficientDynamics banner, except in a shiny new MINI wrapper.

The Auto Start-Stop is one part, but another key ingredient in MINI’s Minimalism ideology is the regenerative braking system, which recoups the car’s kinetic energy during deceleration and converts it into stored electrical energy.

Similar systems are used by hybrids and battery-electrics to top up their batteries, but unlike a hybrid, the electrical energy generated by the Cooper D’s braking system isn’t fed back into an electric motor. Instead it’s used to charge the battery and reduce load on the alternator. With the alternator not required to run all the time, drag on the engine is reduced and more power is freed up to be sent to the wheels, hence improving fuel economy.

The same principle is applied elsewhere on the engine. The water pump is electrically-driven rather than being connected directly to the crankshaft, which allows it to run only when it’s needed and consume the minimum amount of power required. The oil pump is similar, pumping only the volume of oil required by the engine and nothing more, saving up to 160 watts of energy in the process.

The electric power steering operates on a similar on-demand principle, and a low-friction crankshaft also improves efficiency. But aside from all the low-drag ancillaries, the Peugeot-Citroen sourced 1.6 litre diesel is already a pretty economical beast.

An all-alloy common-rail diesel with direct injection, variable cam timing and a twin-scroll turbocharger, the 1.6 litre oil burner produces 80kW at 4000rpm and a handy 240Nm of torque at just 1750rpm - with an overboost function upping torque to 260Nm when the pedal is pressed to the firewall. It’s grunty, to say the least, and with the Cooper D weighing just 1090kg empty, it doesn’t need that much power to pick up its skirt and run.

And run it does. For a car whose primary focus is fuel efficiency, the Cooper D is also a pretty sprightly machine. During our first drive, we took it on a loop that incorporated some CBD traffic, inner-suburban roads and a touch of freeway, and it felt great on all of them.

Yeah, there’s a small serving of diesel clatter from up front, but its certainly nowhere near as agricultural as diesels of old. It’s certainly quick for a diesel of its size too, with the 0-100km/h sprint dispatched in 9.9 seconds – the fastest in its class.

But lay off the accelerator a touch and you begin to see what the Cooper D is all about. The turbodiesel provides oodles of low-down torque, and getting up to speed is a relaxed and effortless process. Nestled within the tachometer is the Shift Point Display (another Minimalism gadget), which prompts you to change up or down a gear to maximize economy. It’s a little hard to spot, but you quickly become accustomed to glancing down to consult it.

The Auto Start-Stop works a treat in the inner suburbs, but venture out on the highway and the MINI Cooper D has one more trick up its sleeve. A streamlined underbody panel greatly reduces drag at high speed, and the tall gearing of the gearbox enables the D to hit a highway fuel consumption figure of just 3.5 l/100km – which we achieved on our test.

It’s a comfortable and quiet place to be in, and with its incredible fuel economy MINI says it’ll take you from Melbourne to Sydney on a single 40 litre tank of diesel. If you’re looking for a thrifty long-distance cruiser and you don’t need the space of a sedan, you can’t do too much better than the Cooper D.

Off the highway and onto some slightly twisty roads, the Cooper D demonstrates that it hasn’t lost any of MINI’s trademark handling nous during the transition to diesel power. Alloy control arms cut overall weight and unsprung weight with the latter leading to improved handling, while the all-alloy diesel engine doesn’t make the D a lead-tipped arrow. It turns it well, feels composed over bumps and expansion gaps and it seems just as nimble as the regular Cooper, so there’s no compromises in this department.

While the D’s handling feels more or less identical to its petrol-powered brethren, it also looks the same too. Sure, there are subtle differences with badging, the intercooler intake and a slightly more pronounced bonnet bulge, but it still bears all the hallmarks of the new MINI’s design, and we love it.

In summary, it’s less expensive than a Prius, prettier than a Prius and more efficient that a Prius. So it’s the better car then?

Well not necessarily. The Cooper D is the apple to the Prius’ proverbial orange – you can’t compare them. The Cooper D is without doubt the more efficient of the pair, but it’s also much smaller and less practical. They target different markets, and when the new Prius arrives later this year with a claimed consumption figure that’ll match the Cooper D, the choice will probably boil down to what’s more important – practicality, or the thrill of the drive.

We’d take the latter, and that’s something that’s evidenced by the numbers obtained on our own fuel-economy test cycle. Over a mix of city, suburban and highway driving, we managed to record an average fuel consumption of 5.7 litres per 100km – a figure that’s largely thanks to my heavy right foot.

But considering how much harder I drove it than most normally would, that’s an admirable result. Not only that, but the A/C was on and the radio blaring, too.

The Auto Start-Stop system alone saved a lot of juice, and it’s easily worth the $2650 premium over the petrol-powered Cooper. It’s a pity you don’t get it with an automatic transmission, but the boffins at BMW are working on that.

The MINI Cooper D is on sale in Australia now in either base configuration or Chilli spec. The Chilli gets 16-inch alloys, leather sports seats, foglights and a 10-speaker sound system. Cooper D pricing starts at $33,750 for the base manual and rises to $36,100 for the six-speed auto, while the Cooper D Chilli costs $37,350 in manual guise and $39,700 for the auto.