Driven: Honda's Clarity hydrogen car
So what's the fuel cell hydrogen Honda Clarity like to drive?
Being electric it is quiet.
At one point, a pedestrian stepped off the kerb right in front of me because he had not heard it coming.
Like other electric cars, there are no gears.
The electric motor simply spins faster and faster as you push the accelerator.
And because of the way electric motors work, the power is there straight away.
There is no need to bring the revs up as you would in a petrol engine.
Another advantage is that electric motors are smaller than their petrol engine equivalents.
That means the space at the front of the car can be smaller.
On the other hand, the pressurised fuel tank does take up space in the boot, but there's still a decent amount of space left, but not as much as you would expect in a car of its size.
And of course, when you look at the exhaust, all that appears is water.
Nevertheless, some sound a note of caution as to the green credentials.
"The real issue with hydrogen is how we're going to produce it, how we're going to store it and how we're going to distribute it to get it into filling stations," says Chris Crean from Friends of the Earth.
"When we've done that we have to do a full life-time analysis as to how that is going to help us to meet our climate change objectives, our bio-diversity objectives and also the use of resources.
"If it doesn't enable us to meet our international commitments then we do not see this as a technology of the future."
Hydrogen filling stations would obviously be needed for motorists to get around, but long term Honda says people could make their own fuel at home.
They see people having special boilers installed to produce hydrogen from natural gas, which could then be used to fill the car.
Heat would also be generated, which could be used around the home.
And so to the big question. Even if you cannot use one in the UK at the moment, how much would it cost if you really did want one?
Well Honda has not put a price on the car because it is not selling it, insisting it could cost "a couple of hundred thousand pounds" if I wrote it off whilst driving.
Clearly, there are a lot of things to overcome before you or I buy one.
We have had similar problems before - more than 100 years ago to be precise.
In the late 19th century there were dozens of electric taxis driving around London.
At the time they were considered more advanced than their petrol equivalents.
But it was much easier to transport petrol around the country and set up fuelling points than it was to do it with electricity.
And in case you are interested in seeing the old electric cars, until Sunday they are on display at Clarence House in London. It is a rare outing from their normal home in the Science Museum's storage warehouse.