A STOP and start system has been introduced by Vauxhall on its Corsa models and it's turned the supermini into an urban street fighter for the eco-conscious driver.

Vauxhall is claiming an average of 70 miles per gallon from the new 1.3-litre diesel Corsa ecoFLEX but when we put it to the test the results were astonishing.

On a 77 mile run taking in all types of conditions we managed to clock up an incredible overall figure of 79.8mpg according to the car's onboard computer.

Many drivers struggle to get anywhere near the manufacturer's declared average mpg but with the new Corsa they could see some surprising achievements.

Our route headed east from Leeds to Selby then north to York and Wetherby before returning to Leeds at the start of the evening rush hour.

It took in A and B roads, dual carriageways, country lanes, a stretch of motorway and city centre traffic.

Although by no means a scientific experiment this was designed to test the Corsa in real world conditions.

Where possible we drove at the speed limit and observed the two second rule as an aid to safety and anticipation using a light touch on the throttle.

Within a few miles after setting off the Corsa's average fuel consumption readout was showing an mpg figure in the mid-60s. That would rise to 80.5mpg by the time we reached York.

Impressive stuff, especially as the flat landscape towards the Yorkshire Wolds required the throttle at all times.

In the congested centre of York the stop/start system came into its own, cutting the engine whenever the Corsa came to rest at traffic lights or junctions. In the 15 minutes it took to cross the city the engine was off for more than a quarter of the time - an obvious fuel saver.

Stop/start technology is becoming an increasingly popular fuel saving device but is still fairly rare on small cars.

The stop/start operation on the Corsa is effective and feels quite natural once you become used to it.

A special feature allows the driver to select whether or not to keep the air conditioning running while the engine is off.

With other stop/start systems leaving the air con on causes the engine to fire up as soon as the car's sensors detect the drain on the battery is becoming too great - reducing the fuel saving potential.

On an autumn afternoon we elected to run with the air con set to turn off with the engine and astonishingly the mpg readout fell only to 78.2 by the time we left the city.

Higher speed work on dual carriageways and a stretch of motorway kept consumption hovering around the 79 mark before joining the queues into Leeds where again the stop/start came into its own.

By the end of the run we had covered 77.3 miles at an average speed of 29mph, used less than a gallon of fuel and recorded an overall mpg of 79.8 - almost 10mpg more than the official figure.

The stop/start Corsa has CO2 emissions of 105g/km which makes it exempt from road tax when bought new.

In terms of CO2 output it is not the lowest in the Vauxhall line up but this Corsa is specifically designed to be most efficient around town.

Vauxhall says the system makes the 75PS 1.3-litre diesel engine seven per cent more economical in traffic and claims the car can average almost 60mpg under such conditions.

The stop/start version we tried costs £13,695 - £700 more than the cheapest diesel Corsa -  and comes with air conditioning as standard.

If needed the eco mode can be switched off and driven hard the car can accelerate 0 to 60 in 13.9 seconds with a claimed top speed of 101mph which is the same as the conventional model.

At the moment the Corsa is the only car Vauxhall is offering with stop/start but it is likely the technology will be rolled out to include other ecoFLEX models in its line up.