I had intended to calculate the carbon footprint of a week’s travel to Ireland.

At first it looked fairly straightforward, 1,800 kilometres at 218 grams per kilometre in straight road travel divided by the seven seats fitted in the Citroën C8.

But then there is the Irish Sea crossing on the Stena Explorer high-speed catamaran, capable of carrying up to 1,500 passengers and 375 cars or freight at 40 knots. What’s your slice of that carbon cake?

And what’s the alternative? Coach to Birmingham Airport, say, fly to Knock in the west of Ireland and hire a car there.

And before someone suggests cycling, with the average age of everyone inside at 65 — even with a keen ex-cyclist on board — that was not an option.

I quickly gave up trying to work out what is the most carbon-efficient method of travel, but I do know what is the most comfortable.

And for my money, bowling along motorways in armchair-like comfort surrounded by as many of your personal creature comforts as you like in a light, bright, powerful MPV takes some beating.

Space is what counts when you are buying a people carrier and on that score Citroën’s C8 is a winner.

The C8 comes with seven seats as standard, and the option of eight on some models, so shifting people and their luggage is a breeze. Citroën uses a rail system to mount its full-size rear seats, so each one can be moved around, or completely removed if desired to massively increase luggage capacity.

The C8 was given a boost this year with a style update to the whole range, the choice of two new metallic colours and, more importantly, the fitting of a new 2.2-litre turbocharged diesel engine on the SX and Exclusive models, delivering 173 horsepower, and a huge amount of pulling power.

The restyle incorporates chevrons at the front and rear, bringing them in line with other models in the Citroën family, as well as a new-look grille, additional exterior chrome inserts, and dark tinted windows and tailgate on top-of-the-range Exclusive models.

Citroën has extended the style treatment to the interior too, with enhanced materials, soft-touch finishes and further chrome inserts for a polished look.

Exclusive models also get 16-inch alloy wheels, leather seats as standard and front and rear parking sensors, which are a boon on such a large vehicle.

Anyone who thinks they can shed light on the real comparative carbon costs of travel is welcome to get in touch, but in the meantime I will stick with driving.

Auto facts Citroën C8 2.2 HDi Exclusive

  • Price: £28,395
  • Insurance group: 15A
  • Fuel consumption (Combined): 34.4mpg
  • Top speed: 122mph
  • Length: 472.6cm/186in
  • Width: 185.4cm/73in
  • Luggage capacity: 16.9 cu ft (three rows of seats in place)
  • Fuel tank capacity: 17.6 gallons/80 litres
  • CO2 emissions: 218g/km
  • Warranty: 3 years/60,000 miles