Owners of the super-frugal Volkswagen Polo Bluemotion won’t need to pay road tax, because the diesel hatch emits just 99g/km of CO2.That makes it cleaner than any current hybrid – Toyota Prius included – and one of the cleanest combustion-engined cars on sale.The Bluemotion uses a specially tuned 1.4-litre three-cylinder turbodiesel engine with intercooler and exhaust gas recirculation for maximum efficiency.It mixes this with a special five-speed gearbox and carefully honed aerodynamics to make drag as low as possible, and returns a remarkable 74.3mpg. If you go for the cheaper version, that is. That’s because the Bluemotion will be available in two trims; Bluemotion 1 and Bluemotion 2. The latter gets air-con, rain-sensing wipers, remote locking and leather trim on the wheel, gearknob and handbrake. Those additions push the Bluemotion 2’s fuel economy down to 70.6mpg, and its CO2 output to 104g/km – still less than a Toyota Prius. They also push the Bluemotion 2 out of tax-exempt Band A road tax, but only just.The Polo Bluemotion goes on sale in October. A three-door Bluemotion 1 costs £11,995 and the Bluemotion 2 £12,845. The five-door models are £500 more.