“No, no, go to the head of the queue,” insists our instructor, gesticulating firmly up the narrowing triangle of sliproad we’ve been trying to leave, to join the densely packed traffic on our left. We had assumed that our first eco-driving lesson was going to teach us how to be more considerate drivers, but instead we’re being taught techniques that would make a minicab driver blush. We do as we’re told and press nervously ahead in our non-lane, girding ourselves for battle with the white van we’ll shortly be needing to cut in front of.

Conserving fuel is, we’re learning, all about keeping moving when you might otherwise stop. Building up momentum uses fuel, slowing down wastes it. And the least thirsty way to get from A to B is at a constant speed with the motor turning inside its efficiency sweet spot – so that’s what we’re aiming for. Constant, steady speed. Early braking. Choosing the clearest bit of road and trying to avoid slowing to a halt. Politeness? We don’t do that.

This is our second run around a loop of crowded Parisian thoroughfares: over the Pont de Sevres, along the Rue de Tryon and Route de Vaugirard, aross the Ile Staint-Germain via the Boulevard des Iles, along the Quai de Stalingrad and back to where we started. Just over 5km or three and a bit miles, it takes 13 minutes and 29 seconds to complete, yielding an average speed of 14mph. At our first attempt, that is, with our hawk-eyed instructor simply studying the readouts on the laptop he has plugged into our Renault Clio Eco2 diesel’s dashboard. With what we thought was careful and prudent driving, we managed 40.6mpg on that first run. With which we were pretty pleased.

Second time around, our instructor is keen to point out all the things we did wrong. All the downhill slopes where we failed to entirely lift off the gas. All the red traffic lights where we foolishly stopped instead of braking early, so that we might roll over the line in second gear just as the colours changed. All the clear bits where we neglected to select fifth gear at 30mph. All the times when, like some red-misted racing driver, we let the engine stray beyond 2,000rpm.

At the end of lap two we can feel the difference even before the stats are presented. Cutting up that white van meant it took us 90 seconds less time to complete the circuit – making it 1.5mph faster. We stopped half as frequently, braked half as often, and spent half as much time standing still. The engine completed 15 per cent fewer revolutions and drank 25 per cent less fuel. The headline figures are 53.6mpg and 116g/km of CO2. Around town. With three people in the car. We are suitably impressed.

Our brief lesson is just a taste of a new Eco-Driving course that Renault will soon be laying on for its fleet customers, showing them just how much fuel – and thus cash – can be saved if drivers learn a few simple techniques. So don’t be surprised if you notice an upswing in Lagunas and Meganes sliding cheekily ahead of you over the next couple of years. The lessons will be particularly pertinent when Renault starts selling its electric cars early next year, where driving style can have a very large impact on the finite range available from an EV’s battery.

In our diesel Clio, our instructor was confident that within a few more loops he’d have got us under 100g/km and we don’t doubt him. The car’s official combined cycle rating is 98g/km.

No doubt you’ll have read lots of road tests where motoring journalists bleat that the official figures of frugal eco-cars simply can’t be achieved on real roads. Well, they’re all wrong. As we learned in Paris, they just aren’t driving right.

Thanks to Renault for providing our lesson - visit its Sustainable Mobility site for more eco motoring updates.