SPORTS cars built by BMW will soon be the first in the world to feature start-stop technology.

Gadgetry that saves fuel by switching off the engine at idle and firing it up again when the accelerator is pressed is to be fitted as standard on M3 models.

Every version in the German firm's line-up of go-faster mid-size cars will come with the equipment from the end of next month in a move to cut tailpipe emissions and boost running economy.

‘It will be the first time that a BMW powered by an engine more than four cylinders has featured this technology and it is not available on any other high performance car,' said a spokesman.

The specification change means exhaust emissions of the M3 saloon are cut from 285g/km to 263g/km and average fuel economy rises from 23.7mpg to 25.2mpg.

At the same time, the M division is introducing a new competition package to enhance the driving dynamics of the M3 Coupe.

Featuring revised controls for the electronic dampers and stability system, lowered suspension and exclusive 19-inch light alloy wheels, it adds £3,315 to the £52,730 cost of the car.