When specified with the 335bhp 55 TFSI 3.0-litre petrol engine, the A6 responds enthusiastically whenever you ask for a burst of acceleration cracking 0-62mph in 5.1sec. However, the diesels will be much cheaper to run, and so will the similarly lively plug-in hybrid if you top up its batteries fairly regularly. Although claimed economy is mid-thirties, you’ll have to drive very carefully to crack 30mpg.