Having a high sixth ratio mated with a lively 2.0-litre engine gives our SE version the potential to stretch a gallon as far as 53 miles in relaxed driving.
Pressed harder, the return is more than 47mpg, a significant achievement in a car with the versatility to offer the loading potential of a van (54.3 cubic feet) or the room for up to seven occupants.
But with the latest example of the turbocharged HDi engine under its sharply-raked bonnet, the SW does more than merely make the most of expensive fuel.
With the muscle to reach the benchmark 62mph from zero in less than 11 seconds and the brawn to achieve 122mph all-out (if you dare), this is entertaining transport that drives so well that it prompts you to ponder the petrol-versus-diesel question all over again.
Several factors need to be considered to arrive at the answer, of course, but in average use, a bonus of up to 15mpg over the SW’s petrol-driven equivalent suggests this diesel car can boast vastly superior running costs in the long term.
There’s no doubt that high gearing makes a big contribution in this respect, and because it allows the motor to operate at little more than 2,000 rpm for most of the time, the long-legged sixth speed also plays a key role in reducing mechanical noise to little more than a whisper as the engine lazes along at motorway cruising speeds.
To that extent, the SW is delivering everything promised by its specification sheet. However, it is exceeding expectations in another respect, thanks to a panoramic glass roof that allows this compact multi-purpose model to provide most of the pleasure of open-top driving with none of the drawbacks.
Covering most of the roof, the 1.33-metre expanse gives the interior a remarkably light and airy feel – and even helps make the gloomy days of winter more bearable. In brighter conditions, a powered blind can cover the glass to prevent the build-up of heat, so this is a genuine best-of-both-worlds arrangement.
And plenty of storage areas, power sockets for accessories and air conditioning that also cools the glovebox means the SW is particularly equipped to cater for family use, which is probably why the design has become a popular choice in the user-chooser sector.
With a lower roofline, the Peugeot drives better than most MPVs, a factor that makes it an attractive proposition to higher-mileage business drivers – even without that super-high sixth ratio.
Model: Peugeot 307 SW 2.0 HDi SE
Price (OTR): £17,800 (£18,539 as tested)
CO2 emissions (g/km): 148
Company car tax bill (2006) 22% tax-payer: £61 a month
Insurance group: 10D
Combined mpg: 50.4
Test mpg: 50.24
CAP Monitor residual value: £4,975/28%
Expenditure to date: Nil
Typical contract hire rate: £327
Figures based on three years/60,000 miles