It’s often cited in these pages that the rising cost of petrol and diesel means fuel economy is increasingly becoming a deciding factor when choosing a new car. In response, manufacturers are bandying about consumption figures of over 80 miles-per-gallon (mpg) – but just how realistic is it for a ‘normal’ driver to match a car’s published mpg? The seeds of doubt were first sown back in March, when a study by lobby group Transport & Environment (T&E) suggested car manufacturers were manipulating fuel consumption and CO2 emission tests to bump up cars’ performance figures by an average of 23%. So let’s say you cover around 12,000 miles each year, you’re in the market for a fuel efficient car and plump for a particular model on the back of its promise to return a whopping 83mpg. This means you could expect to pay £936.60 in fuel, based upon the average price of a litre of diesel at 142.5p, as it is today. However, if the figures have been bumped up by 23%, this means the car may actually only be capable of 63mpg and so same annual mileage will cost £1,233.94 – which represents a completely unexpected increase of £297.34. So is it possible to get anywhere near your car’s estimated mpg? To try and answer this, we first need to look at how manufacturers test their vehicles.