Our weapon of choice was a mkII Ford Focus, one of the biggest selling family cars of the last 10 years and one of the most common cars on the road today.
Now we did things properly on this drive, we went on a 20 mile circuit, made up of motorway and a little bit of town driving.
After all it is likely to be in the long haul journeys where the cost of running Air Con is likely to be at its highest.
We did a couple of runs, one with Air Con, one without and took the average MPG from both runs to hopefully give us an answer if it is all that bad.
And to contrast to my usual driving style, all the revs were kept down making this one of the most boring drives of my life. What we do for consumer advice!
So you can’t say we weren’t fair!
So after 15 miles and some very shrewd eco-driving our Ford Focus 1.6 returned a very respectable 42mpg.
A quick stop, a push of the Air Con button and another lap of our eco-circuit and we had an answer, it returned a still impressive 39mpg, a difference of 3mpg.
So in actual fact, the industry is right on this one with our engine showing a loss in efficiency of 7% almost bang in the middle of the 5-10% the experts predict.
This whole 10% less efficient thing sounds like it might be a lot but in perspective it really isn’t that bad.
To talk the international language of money, this means you spend about an extra pound per 100 miles. Not a bad rate to stop yourself burning off as much fluid as your car burns petrol.
Ok yes things do change from car to car and I am sure that for some it may be more expensive, but this is all about averages and there are few cars more average than a Ford Focus.
So then it is up to you whether you are pinching the pennies so much that you want to save that extra £1 of fuel to take the car down the shops or whether you prefer to get out of the car without embarrassing sweat patches.