Surprisingly few modifications need to be made to let engines run on hydrogen. The fuel injection system has to be redesigned to cope with a larger flow rate and the fuel tank needs to be able to cope with either liquid hydrogen at very low temperatures or gaseous hydrogen at high pressure.

Because of the complexity of creating a cryogenic fuel tank, which would add weight partly because of the need for insulation, manufacturers currently favour the high-pressure option. Filling stations store the gas in pressurised containers, and to refuel the driver attaches a hose to his fuel tank, creating an airtight seal, before a valve opens to allow the gas through.

Despite the complications involved in handling the fuel, hydrogen engines are barely different from the ones we know and love today. A petrol engine modified to use hydrogen loses only 10% of its power, while a purpose-built hydrogen internal combustion engine produces as much power as its petrol equivalent.

It sounds and feels just as good, too. So once hydrogen becomes more widely available we’re likely to see two sorts of cars: quiet, efficient but boring fuel cell ones, and for the enthusiasts silky sixes, muscular V8s and liquid V12s. Just like today, in fact, but emitting only water. And great exhaust notes!