Scientists said on Tuesday they have developed a way of extracting hydrogen from oil without releasing greenhouse gases - a breakthrough they hailed as a "silver bullet" for cleaner energy and the climate.

Unlike petrol and diesel, hydrogen produces no pollution when burned. It is already used by some car manufacturers to power vehicles and may also be burned to generate electricity. 

But until now the wide-scale roll-out of hydrogen technology around the world has been prohibited by the high cost of separating it from hydrocarbons. 

Currently the vast majority of hydrogen used for vehicles is derived from natural gas, the extraction process of which produces planet-warming methane.

Now a group of Canadian engineers say they have come up with a method of getting hydrogen directly from oil sands and oil fields, while leaving carbon dioxide and methane in the ground.