As the owner of a Nissan Leaf, one thing is certain - you won’t be doing any long journeys. So when I needed to head up to Lancashire, via the south Midlands, back to London and then straight up to Stansted airport, I needed an internal combustion engine.

Editor-in-chief Steve Cropley kindly lent me the keys to his Mercedes S350 Bluetec, which comes equipped with an impressive V6 diesel engine and a very big fuel tank.

I headed up towards Stratford on a Saturday evening from the southern end of the M40 and was amused to, as the traffic started to thin out, the Merc flashed up an amber warning that the car had just 75 miles range left, which is more than the Leaf usually has after a day’s commuting.

I filled the car at Oxford services. It swallowed £108 of diesel. However, as I cruised back up the empty M40 at an indicated 80mph, the trip computer’s predicted range was steady rising. From a 550-mile range after filling up, the distance-to-empty steadily rose to 670 miles, suggesting I might have discovered perpetual motion.

The S350 has clearly been optimised for the 80mph autobahn cruise. The dash has a scrolling horizontal bar showing instantaneous fuel consumption. Hit the right speed and throttle opening and the bar shoots rightwards, up to the 40mpg limit.