Production of e-diesel isn’t merely a matter of mixing all the above together, of course, but Audi has made the process fairly efficient. Water is heated to form steam, which is then broken down into hydrogen and oxygen by means of electrolysis at a temperature of over 800 degrees Celsius. The hydrogen then reacts with the biogas-derived CO2 under pressure and at high temperature, forming a liquid Audi calls “blue crude”.

Blue crude can then be refined to make ignitable e-diesel, which can be mixed with conventional fuel or used on its own. It’s totally clean, the only use of fossil fuels being in its production.

The car manufacturer has only recently started production of the fuel, but plans to produce over 3,000 litres (not a vast amount - but we're talking about a whole new type of fuel here) in the coming months – and it claims synthetic petrol, or “e-gasoline”, isn’t too far off either. We could be looking at a future fuel that lets you tear around in your A3 without feeling guilty about killing the planet the entire time.

We'll update this story with more detail as we get it.