Sitting behind the wheel of any Porsche tends to produce a gentle self-satisfied smirk.

But driving a Panamera Diesel delivers a simple, straightforward feeling of smugness.

Stretching luxuriously around you is the whopping four-seater GT bodywork, sumptuous leather interior and more buttons than you can shake a stick at, while under the bonnet lies a secret weapon.

For the power source of Porsche’s grand touring Panamera is a 3.0-litre V6 diesel delivering 250 horsepower and the ability to cover more than 43mpg in day-to-day driving. That, says Porsche, is enough to take four passengers in comfort from Land’s End to Loch Ness without refuelling.

Go for the optional lower rolling resistance tyres and Porsche says 44.8mpg is on the cards.

In Porsche Gran Turismo terms, life doesn’t get more economical, or much more affordable, than that.

In terms of price, the rear-wheel-drive diesel model sits just above the entry-level V6 petrol version, using a smooth, willing 3.0-litre diesel mated to an eight-speed Tiptronic gearbox, lifted directly from Audi.

All this combines to deliver a thoroughly relaxed cruiser, which is happiest when stretching its legs on a long, fast run. Quiet and refined, at motorway speeds, with the accelerator under little pressure, it is difficult to tell that you are in a diesel-powered car.

The test car came with optional 19in wheels and on twisting country roads the steering is nicely weighted, matching a firm ride with superb body control. To help drivers get the best out of the car, buyers receive a complimentary course at the Porsche Experience Centre, in Silverstone.

Around town, stop/start technology kicks in to help boost fuel economy.

The interior is a simply gorgeous place with superb comfort, head and legroom, not only for those in the front seats, but also the two firmly contoured individual seats in the rear. Standard specification includes bi-xenon headlights, touch-screen satellite navigation and audio controls, cruise control and a Porsche Vehicle Tracking System.

Any drawbacks are shared by the other models in the Panamera range. It is not that easy to see out of, but a battery of parking sensors fore and aft do their best to keep the bodywork intact and those whopping great alloy wheels safe from being scratched on kerbs.

Porsche drivers looking for the ultimate ‘green’ Panamera might be tempted by the hybrid version, which is more powerful, faster and emits lower carbon dioxide emissions than the diesel. But all that comes at a much heftier price – an extra £24,000.

Auto facts Porsche Panamera Diesel

  • Price: £62,134
  • Insurance group: 20 (1-20)
  • Fuel consumption (Combined): 43.5mpg
  • Top speed: 150mph
  • Length: 497cm/195.7in
  • Width: 193.1cm/76in
  • Luggage capacity: 15.7 cu ft
  • Fuel tank capacity: 17.6 gallons/80 litres
  • CO2 emissions: 172g/km
  • Warranty: 3 years/unlimited mileage