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.

And competition is fierce. Most of the old boys are previous mpg record breakers. Instead of reversing out of a space when leaving checkpoints along the route, the car is pushed. Rather than stop for oncoming traffic, the kerb becomes the road. You get the idea…

One team even switched off the car's engine at the top of every hill, which, not only dangerous, also disengages the trip computer, so they've managed to shave around 12 miles off the route. Tut tut.

Our Jaguar, of course, has been delightful, especially the eight-speed automatic gearbox, which is extremely smooth and wholly competent. Apart from a sore back from fairly unsupportive seats, the trip has been happy camping. Unlike me: during a stint as navigator I’ve just taken us the wrong way, which has added two miles to our journey. Bugger.

More from us later.