Launched on the all-new Ford Mondeo, the new European-edition Ford Focus on sale in January will also be fitted with the Easy Fuel system as standard.

The news comes as UK breakdown services deal with twice as many incidents of motorists putting the wrong fuel in their vehicles as a decade ago.

"Ford's intention is to isolate the danger of engine damage to all customers," said Ford fuel systems engineer Stefan Buro. "With Easy Fuel, we have developed a method for error-free handling, especially for the coming generation of quiet diesel engines, where the only things customers notice are good performance and excellent fuel economy."

The Easy Fuel system, with a patented mis-fuelling inhibitor, consists of a sealed filler pipe insert and fuel nozzle locator that guides the nozzle to the tank opening. The insert contains a mechanically operated diameter detector which only allows the larger diesel fuel nozzle to be inserted into the filler pipe and locks out the thinner petrol nozzles.

Unlike a petrol engine, which compresses a mixture of petrol and air, diesel engines compress just air before diesel fuel is injected into the cylinder and the fuel is ignited. Pouring petrol into a diesel engine can cause damage to the fuel pump, the high-pressure injection system, as well as trigger other serious engine problems and four-figure repair costs.