Measuring 208.4cm or 6ft 10in from the tip of one triangular mirror to the other, Vauxhall’s Insignia EcoFlex turns out to be the widest car we’ve yet tested for this blog. We can tell it’s the widest because it wouldn’t fit through the narrow gate to GreenMotor towers until one of its Spock-ears was folded away. And with the UK’s air supply arriving direct from the arctic at the time, we found ourselves wishing for the frippery of power folding. Dropping a window to shift a mirror with a frigid fingertip is not exactly a route to winter warmth.

There’s no denying that the Insignia is a family sized motor, so we are duly impressed that it turns in an official CO2 score of 136g/km. OK, so that’s not exactly vying with the Toyota Prius to be crowned the cleanest full five-seater, but 54.7 miles for each gallon of your finest diesel, in combined cycle theory at least, is not too shabby.

The EcoFlex badge on the rump adds about £540 to the price of an Insignia – the green label can be added to any trim level except the sport-leaning SRi. As well as a the shiny label you get a particulate filter, eco tyres, a flat undertray, a remapped engine, dropped suspension, longer gears and an insistent reminder on the dashboard telling you to change up.

Collectively, these tweaks can cut fuel consumption by about a tenth. Along with savings in road tax, this means the average private punter will pay off the EcoFlex premium only if they keep the Insignia for three years or at least 35,000 miles. That’s assuming diesel doesn’t suddenly hockey-stick upwards from its current £5-a-gallon level. Company car buyers, at whom the Insignia is squarely aimed, can start to save real money after as little as 12 months.

Going back to those door mirrors, they are a hopeless shape. Wide at the inside but pointed and narrow at the tips, they provide a great view of nothing at all. We don’t like them, particularly given that rearward visibility in our five-door test car was abysmal. Reversing sensors would be a sound investment, X-ray vision a help.

We’re wary of long gearboxes in eco-label specials - some succeed in making their motor truly horrid to drive. Thankfully the Insignia is immune to this malady - almost. Around town we found ourselves using gear three out of the six available, when we might normally choose fourth, but third keeps the car on form around 30mph and doesn’t hobble the fuel consumption too much. On faster roads the gearbox feels more natural, and will even pull up minor motorway inclines in sixth. Whatever our steady speed, there was always a gear to keep the gruff motor murmuring along quietly and the mpg meter happy.

We did manage to virtually stall the car at one traffic light, which obligingly turned from red to green just as we rolled up. As we were still moving we slotted into second and expected to glide away on a wave of torque, instead provoking a tuberculean coughing fit. Long gears and the real world don’t always align, even when you have almost 160bhp and 350Nm on tap, but we soon got used to the need to slip the clutch in such circumstances.

High points of the Insignia include its lovely interior, excellent forward visibility, great seats with wide adjustment, super automatic wipers, a nice electronic handbrake, helpful follow-me-home lighting and puddle lamps, beautiful interior illumination and an overall feeling of well-built solidity.

Turn-offs include the Scrabble-bag of buttons on our car’s centre console, which we suppose we’d eventually learn to tell from each other, dusk-sensing lamps that sensed dusk beneath every passing cloud, and a dismal photochromatic rear-view mirror that reduced the already narrow rear view to dim pointlessness at night. We prefer being dazzled to not being able to see behind at all.

The steering wheel is nicely sculpted but is fairly tight-lipped in its messages about front-end traction, and the brakes are similarly mute. The suspension, which has been lowered by 10mm in pursuit of reduced frontal area, feels well sprung but somewhat under-damped. Cornering is relatively flat, surface gremlins are suitably smothered, but you will occasionally feel you are piloting a boat across a choppy sea.

Lasting impressions? The Insignia feels like a lot of car for the money – our Exclusiv Nav EcoFlex came with Bluetooth, a fine built-in satnav system and the kind of Xenon headlamps that peer around corners, yet cost just a fiver over £22,000 on the road.

Of course it’s a Vauxhall, so it holds its value like a Christmas cracker. A quick riffle through the approved used scheme produced a 2009 model with less than 6,000 miles on its clock, for £15,499. That really is a lot of eco car for the cash – widthways at least.