Not every motor show has a theme, but if there’s one to come out of the halls of Tokyo’s Big Sight today, it’s hydrogen fuel cells. They’re in the news anyway, of course, with Toyota’s Mirai making headlines on the back of its UK launch recently, but it just seems that every hall in Tokyo has a hydrogen story to tell.

Perhaps most tellingly of all, this really feels like the show when fuel cell cars aren’t just pie in the sky; they’re either about to go on sale, or there are concrete plans to get them into customers’ hands in the next 18 months. Okay, so Mercedes’ lounge-seat creation is probably a bit far-fetched - but isn’t it amazing that the next Lexus flagship looks set to have a fuel cell edition?

And then there’s Honda. I tried the FCV Clarity the other day and it’s a really remarkable thing - but it’s even more impressive when you hear that the first 200 cars will be leased to Japanese customers in 2016. That’s nearly three times as many examples as the car’s predecessor, the FCX Clarity, sold in its entire history. And the leasing bills will be not quite mainstream but not exactly ‘sell a kidney’ material: around £800 per month, over a four-year deal.

The challenge, according to Honda boss Takahiro Hachigo, is to further reduce that monthly cost and develop technologies that can be mass-produced. And I reckon he’s right. It’s no longer the theory that’s holding these things up; it’s the practicalities.