As I write, my co-driver and I are two thirds of the way through this year’s MPG Marathon, the economy driving event that pits drivers against their cars’ fuel gauges.

This year about 25 cars are taking part, ranging from Peugeot’s new 74mpg 3008 Hybrid4 to the brutal (and rather less frugal) Vauxhall VXR8.

We're in the new Jaguar XF 2.2D. Since yesterday, 260 miles have passed by – slowly – with only one third of the tank consumed. In fact, as we follow the route prescribed by the organisers through the south of England, we're beating Jaguar's claimed average of 53mpg by approximately two mpg.

Although it may sound frustrating, keeping a car's revs under 1750rpm is actually quite good fun, especially when approaching traffic lights and roundabouts: stop at either and you've had it, so you have to weave the car through traffic with pinpoint accuracy.