The TV presenter got behind the wheel of an Audi A8 and drove from London to Edinburgh and back on one tank.
He said: “Driving with the window down for instance increases fuel consumption by 5%.
“And to make matters worse, you can’t use the air conditioning either because that does even more damage.
“In a Honda Civic for instance, if you get 36 miles to the gallon normally, you turn the air con on and you’ll get 30 miles to the gallon. You lose 6mpg.
“In fact, you shouldn’t use any electrical gadgets unless it’s absolutely necessary. The heated rear window’s a complete no-no and the heated seats forget it.”
The air conditioning unit has to work hard to bring the vehicle’s internal temperature down to a more manageable level.
Engine power is used to run the air conditioning compressor, which in turn uses up petrol and diesel.
A previous study from Emissions Analytics found that fuel efficiency dropped 6.1% in a hybrid car when the air conditioning was on.
Meanwhile, fuel efficiency dropped by 3.8% for a petrol car and 4.6% for a diesel- vehicle.
However, motoring experts at KwikFit admitted that air conditioning could increase fuel use by as much as 10% in a hefty blow.
They explained: “The compressor requires energy to run your vehicle’s air conditioning system and so will use a small amount of fuel whenever the system is running.
“It could increase your fuel usage by as much as 10%, and the effects are particularly noticeable on short journeys.”
