Volvo S40 1.6D DRIVe Start/Stop

What is it?

This is a fuel-saving, carbon dioxide-staunching 108bhp 1.6-litre turbodiesel S40, that achieves an impressive 104g/km when equipped with £250-worth of optional Start-Stop hardware.

That happens to be the same carbon dioxide figure as for the outgoing, second generation Toyota Prius and it’s usefully lower than the 114gkm achieved by the Focus Econetic whose gene pool it shares.

The Volvo’s 72.4mpg combined fuel consumption is, by odd coincidence, the same as for the new Prius – though the Focus manages 78.4mpg - and it also qualifies in band B for road fund duty besides attracting a low 13percent benefit-in-kind tax for company car users.

So purely on a running-cost basis, this is an attractive car. Without stop-start – curiously, Volvo is test-marketing the S40 1.6D DRIVe in both forms – it scores 119g/km and 62.8mpg combined.

The same figures are achieved with identical hardware in the sister V50 estate and C30 coupe, the neat three-door needing aerodynamic modifications that include under-floor panelling, an extended roof spoiler and a rear diffuser to score the same numbers, alterations that make it look quite sporting.

Aerodynamic mods for the S40 include a partial blanking off of the radiator grille, suspension lowered by 10mm and some rather stylish alloy wheels whose slender cooling slots limit turbulence.

Also included are an intelligent alternator (it mainly charges when you’re coasting and braking), low rolling resistance tyres, a recalibrated engine management system, thin-viscosity transmission oil and power steering that draws less energy.

And your chances of achieving pleasing consumption figures are improved by a gearshift indicator in the instrument pack.

What’s it like?

Driving the Volvo S40 has never been a particularly edifying experience despite its close relationship to the Ford Focus, and in physical terms the S40 DRIVe is no better, and in some respects a little worse.

Its lowered suspension means a less cushioning from a ride that wasn’t great in the first place and the taller gearing requires more shifting, though not to a testing extent.

But, the possibility of achieving exceptional fuel economy figures adds a worthwhile diversion to the driving process, especially as the standard trip computer allows you to monitor your miserliness.

The stop-start equipment has the scope to improve consumption by four to five percent, but there is a refinement penalty, the diesel’s high compression provoking engine shake that’s too apparent on shut-down and start-up.

That may well lead some to hit the stop-start button in the centre console, switch it off and avoid the shudders. The diesel Mini, which shares the same powertrain, suffers the same problem, but not to quite the same extent.

Should I buy one?

If low running costs and doing a bit to avert global warming are your goals, this car promises real gains.

Trouble is, the S40 remains the disappointing car that it has always been, and while its fuel consumption will warm your heart, the driving experience will rarely have the same effect.