And so to the engines. These four-cylinder diesels may never rattle our thrill-o-meter, though we can judge them by more sensible criteria. The BMW is the most powerful, but also the least torquey. Having said that, it delivers its muscle from as low as 1,250rpm, making it the most versatile one here. It’s also the fastest, reaching 62mph a good half-a-second quicker than the other two, helped by the fact that, overall, it’s the lightest of the three. And it lands a solid blow on the others at the pumps, achieving mid-60s mpg on our gentle motorway cruise, which - for once - is almost bang-on the manufacturer’s extra-urban claim.
The A5’s 2.0-litre TDI isn’t far behind, but you’ll have to work more diligently to get close to Audi’s quoted 60.1mpg average. However, it does get on with things quietly, blending into the background more successfully than the Merc’s or BMW’s. This is immediately spoilt by the road noise thrown up by the big alloys. Seriously, avoid these wheels, no matter how much you like their looks. An extra inch of air and rubber would make for a more pleasant life on board, and help make the most of the crystal-clear Bang & Olufsen stereo, should you tick that rather costly box. You wouldn’t spoil your home hi-fi by putting the blender on, so why put up with such distortions in the car?
The Merc has the worst economy, for which we can partly blame the automatic gearbox (a plain old torque-converter, rather than a dual-clutcher). It holds onto gears where cleverer ‘boxes shift up, and even in manual mode - when you take control with flappy paddles - it doesn’t like being told what to do, smudging shifts when you want a crisp change. At least there’s an extra 200cc and a chunk more torque than the Audi and BMW, which helps pull you out of bother when you’re in fourth but want third. It’s also the noisiest engine here, and needs to learn some culture in order to worry the 4-Series.