It sounds like three Welsh fishing buddies have developed the next best thing to a perpetual motion machine. The concept is thus: Fitted to car instead of an exhaust their Greenbox device traps carbon dioxide and nitrous oxide. The box needs to be replaced about every full tank of fuel. “Through a chemical reaction, the captured gases from the box would be fed to algae, which would then be crushed to produce a bio-oil. This extract can be converted to produce a biodiesel almost identical to normal diesel.” Voila! - driving your car produces fuel. After a couple of years of testing and umpteen hundreds of thousands of dollars invested in research it would appear that there is more to this than the usual magic solution that crosses our desks. Of course the devil is usually in the detail.