Audi has revealed A1 and A3 models featuring the same cylinder deactivation systems as its high-performance S and RS models.

`Cylinder-on-Demand' (CoD) technology, which will also be employed in Volkswagen's Polo BlueGT, shuts down the fuel supply to half the engine's cylinders under light throttle inputs and noticeably increases fuel economy.

The two new Audi models will share a 138bhp turbocharged 1.4-litre petrol engine which with the help of the CoD system has averaged up to 60.1mpg under the current official tests. The figure applies to the A1, A1 Sportback and three-door A3, with the five-door A3 Sportback dipping slightly to 58.9mpg.

CO2 emissions are just 109g/km for the two A1s and the lighter A3. The A3 Sportback is not far behind, on 112g/km, but does sit one road tax band higher and costs £30 for a year instead of £20.

CoD technology, which when used with gentle throttle inputs is imperceptible in its operation, is the latest in the Volkswagen Group's efforts to lower the environmental impact of its cars.

Two of the 1.4-litre engine's four cylinders can be shut off or restarted in just 13 milliseconds, making it supremely advanced among its small petrol engine rivals. As standard it is combined with stop-start technology for further increased efficiency.

It is an `intelligent' system that judges how the driver is driving and only deactivates cylinders if conditions are right.

For example, if the sensors detect an irregular throttle usage pattern like on a twisting road or through a set of roundabouts, CoD will not activate. Nor will the system work under engine braking, allowing all four cylinders to support deceleration.

With almost identical fuel consumption figures but no default emissions penalties, the CoD-equipped models represent a significant company car tax saving of around 40% compared to the A1 and A3 diesels, according to Audi.