Motorists are paying hundreds of pounds more than they might expect to fill up their cars because fuel economy figures are overstated, a report claims. And it is some of the cars that trade most on their 'green' and fuel-efficient eco credentials where the gaps between the official figures and reality are greatest, according to the study. It means that at a time of record pump prices, drivers end up spending on fuel bills they hadn’t bargained for. Tests carried out on more than 60 cars in real road conditions by consumer magazine What Car? showed that every vehicle had a lower miles per gallon (mpg) figure than that given in the official statistics. The official figures are compiled using tests carried out in laboratory conditions on rolling roads according to EU and UK government guidelines. At a time of soaring fuel prices, it is these official fuel figures that are highlighted by manufacturers in their marketing material and are a huge selling point in showrooms. But the What Car? experts say the figures are 'flawed' because they do not take account of 'real world' driving conditions. For example, official figures showed the Kia Picanto 1.0 2 did 67.3mpg while the magazine’s own test gave a figure of 41.2 mpg – a difference of 26.1 miles to the gallon. That means the official figure is 63 per cent better than the ‘real world’ test result. For a driver covering an average 12,000 miles a year and paying an average 142.5p a litre (£6.48 a gallon) for petrol, that difference equates to around £730 a year at the pumps. Some of the cars which highlight their environmentally friendly credentials are among the worst performers. A Volkswagen Golf 1.6 TDI 105 Bluemotion – VW’s 'eco' badge – has an official fuel economy rating of 74.3mpg yet achieved only 51.8mpg in the What Car? test – a difference of 22.5mpg. And Toyota’s Prius 1.8 VVT-i T Spirit (built before the recent facelift) scored 70.6mpg in the official tests, but dropped to 52.2mpg in the What Car? results – a difference of 18.4mpg. In an attempt to give a more realistic view of fuel economy, What Car? has launched its 'True MPG' initiative whereby car buyers can log on to a website to check real-world figures. The magazine’s editor-in-chief, Chas Hallett, said: 'With rising fuel prices, the miles-per-gallon issue is high on every motorist’s agenda. Countless car buyers are frustrated that they don’t match the official fuel figures. ‘Our results just go to show how unrepresentative the Government’s fuel testing is. The problem is it is done in a laboratory where cars are not driven like normal people drive them.’ Mr Hallett added: 'Some eco cars are very good around town and in an urban environment. 'But the minute you drive them on a motorway then they don’t do so well. 'Against this background, buying a Toyota Prius may be a perfect choice for some people who drive around town a lot, but not for others who may spend a lot of time on motorways.' Some experts say an added problem is that manufacturers tune their cars to get the best test result in the lab, which undermines fuel economy when the cars are driven on the road. The magazine said that in its tests the vehicles were driven by two engineers over a variety of roads, including motorways and A and B roads, and through towns and villages. By contrast, the official fuel economy figures are obtained in a lab based on what is called the 'New European Driving Cycle'. This involves two tests run in sequence. The first 195-second cycle consists of a series of accelerations in the three lower gears linked to periods of idling repeated four times. The 'extra-urban' element comprises a series of very gentle accelerations and short periods of cruising.