Kia's assembly plant in Zilina, Slovakia, has begun full production of six new petrol-powered Ceed ISG (idle stop & go) models claimed to deliver up to a 15% fuel economy improvement in city driving.

Left-hand-drive cars reach European dealers next spring but the start of right hand drive production for markets including the UK, Ireland, Cyprus and Malta has not yet been set.

Hyoung-Keun Lee, who heads the Hyundai Motor affiliate's international business division, said: "The new ISG models confirm Kia's commitment to creating more environmentally friendly and fuel-efficient production models."

Kia Motors (UK) chief Paul Philpott said: "We want to bring this advanced technology to UK customers as soon as possible but sadly we will have to wait for RHD production to begin."

The ISG system is similar to stop-start systems already on offered by other automakers such as BMW and PSA: it automatically switches the engine off when appropriate when the car stops and restarts it instantly when the driver wants to move on.

The 'official' fuel saving is 6% on the EU combined test cycle.

A new smart starter motor is linked to an upgraded ECU, which monitors the car's status. When the car comes to a stop, the ECU uses information from various other control systems around the vehicle to decide if switching the engine off is appropriate.

A new smart high-efficiency alternator suppresses electric power demand during acceleration and recharges the car's battery during deceleration. As a fail-safe, if the car's battery power drops below 75% of maximum for any reason, or there is insufficient energy available for the next start, the system will temporarily suspend stop and go.

While the car is stationary, if the clutch pedal is depressed, the engine is instantly re-started; the re-start occurs in the time it takes the driver to select first gear, Kia said.

The ISG versions emits as little as 137g of CO2 per kilometre. They also have a new, lighter manual gearbox which more than offsets the additional extra weight of the ISG system components.

This new five-speed transmission, made at the newly opened Hyundai plant in the Czech Republic (which also makes Hyundai's equivalent i30 model on a platform shared with the Ceed), weighs 5kg less than the previous unit and has a new selector mechanism that reduces gear-changing forces. Reverse is synchronised with fifth gear for easier selection and the overall 'feel' of the transmission is significantly improved, Kia said.

Kia will add ISG technology to 1.6-litre diesel Ceed models later this year and it is also destined for other model lines, including those sold outside Europe.