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.