Photograph: Martin Godwin

Luckily, Friday the 13th of June held no nasty surprises for the panel of judges testing the short-listed cars for a new green car of the year award 2008. In fact, the models tested provided the panel with much constructive debate and some enjoyable driving in London's busy traffic. The hardest part of the day for judges was deciding on a final winner from the shortlist line-up.

First up, we were very impressed by the ultra-low emissions of the VW Polo BlueMotion 1, with a CO2 emissions of 99 g/km.

It's a real car, you fill it with diesel and its CO2 emissions are so low Gordon Brown won't bother to charge you any road tax. However, much as this car came close to winning the 2008 award, it wasn't the car we all wanted to take home.

And this became the central dilemma that was debated during the pit-stop coffees of the day - if the award was to go to the greenest car, then it had to be the Mega City electric or Polo BlueMotion, but was this same car that most people would actually buy?

What emerged during our many forays up and down the sunny A4 was that the award needed to go to the greenest car that the majority of punters would actually put on their wishlist.

Eliminating some cars from the shortlist was easier - not because they aren't fantastic machines, but with an award, the timing is key. The Prius, bless its pure synergy drive, still manages to turn heads (and raise hackles for those who dislike its futuristic lines), but it's getting on a bit in design-years, and the next model is due next year.

The Mini too is a delight to drive (if you can work out what all the switches do), but its emissions are not groundbreaking for its size, and its owners don't really reflect the average motorist.

So back to the driving board. For EU regulatory reasons (I won't bore you now), there's a bunch of cars that just squeeze into the road tax band B bracket with 119 gCO2/km.

There's the VW Golf BlueMotion which hits all the right spots for a proper car while managing impressively low emissions, but it didn't tickle the collective fancy of this particular panel. Then there's the Fiat ECO - which started out low on the panel's list, but came through with flying Mediterranean colours. Although it wasn't the collective favourite, it was the real (nice) surprise of the day (we're all still talking about it).

And so the third of the 119 bunch, the BMW 118d, with its EfficientDynamics stop-start and regenerative braking technology (a system which allows the battery to be topped up when the brakes are applied). All the judges have fond memories of this one - sexy sleek lines, sporty feel, smooth acceleration.

No doubt about it, this is the car we all wanted to take home (and "live with" according to one of my fellow judges!). But we had to weigh up the fact that were are on a green car mission, and surely the 118d can't be as green as the rest?

Though we thought the technology under the hood was the bees knees, we had to agree that the BMW's 2-litre, 143 bhp engine would probably encourage driving which would make achieving the test cycle CO2 emissions less likely than in some of the other models in the short-list line-up. It certainly did with us.

And so to the Focus ECOnetic 1.6 TDCi. It was there, pinned to the wall chart all through the day - quiet, unassuming, biding its time.

We talked, we drove, we had lunch. And as the day drew to a close, it slowly dawned on us that we needed to look again at the UK's favourite car. While it doesn't outwardly shout about its green credentials, with a WhatGreenCar lifecycle impact rating of 33/100 and CO2 emissions of 115 g/km, it's actually the best in (small family) class. And to top it all, there isn't a motorist in the land who wouldn't call it a "real car".

With the BMW fading from our collective memory (for now anyway), by 5pm, it emerged that the panel were unanimous that the Focus ECOnetic was this year's winning combination of a car. It provided class-leading low emissions and fuel economy, together with the vehicle performance, size and comfort required (and these days expected) by the majority of drivers in the UK.

The judges also recognised the importance of the Focus as the UK's most popular car, and wanted to formally recognise Ford's achievement in developing one of the greenest family-sized models on the market.

With the greener, fuel-efficient Focus ECOnetic now available in the UK, all new car buyers now have the opportunity to buy a more environmentally friendly car, one that meets the needs and aspirations of the average motorist.

Winner of the 2008 award: Focus ECOnetic 1.6 TDCi ECOnetic (110PS) (115 gCO2/km)

Highly commended: BMW 118d Saloon (119 gCO2/km)

• Ben Lane is the managing editor of WhatGreenCar? and runs a transport and environmental consultancy called Ecolane.