They used to say that there was no substitute for cubic inches.

Well, in the brave new, low CO2, future currently being mapped out for us, there is a substitute for big engines.

They’re called very small engines.

At the Geneva show earlier this week, Renault’s powertrain bosses gave me a glimpse of the under-bonnet shape of motoring to come.

The company is currently working a new modular engine family of three and four-cylinder engines, all of which are 1.2-litres or smaller.

The super-frugal petrol versions will get a combination of direct injection, turbocharging, low friction internals, stop-start and energy-recovery alternators.

Apparently, petrol is set for a sales comeback because diesel engines are becoming increasingly expensive to make. Renault’s engineers estimated that each new level of Euro emissions regulations adds 500 euros to the cost of the engine.

So the Euro 5 regulations due this summer will add 500 Euros to the cost of a typical turbodiesel unit, as will Euro 6 in 2012. These costs will inevitably be reflected in the showroom price.

However, it’s not just the price and increasing frugality of petrol engines that will hit the popularity of diesel. The new Euro 5 regulations have rendered diesel engines rather less refined.

To meet the Euro 5, a reduction in clatter-reducing pre-injections has been necessary, resulting in significantly more engine noise, especially at tickover and when the engine is cold.

Anyway, the upshot is that, by 2015, Renault says 40 per cent of its cars will be petrol powered, 45 per cent diesel and 15 per cent pure electric.

Moreover, the French also told me that across the 2015 Twingo, Clio and Megane model ranges, 85 per cent of all cars sold will have an engine sized between 0.9 and 1.2 litres. 10 per cent will have up to a 1.6-litre engine and just 5 per cent an engine up to 2.0 litres.

So it looks like you’ve got around six years to enjoy even a modest number of cubic inches. After that, the typical new-car engine will look like something your grandfather had in his lawnmower.