Nevertheless, GTC drivers liked them, finding their own way round the refuelling issues, which of course were part of the trial, that was as much about the infrastructure as it was the vehicles. And those funding grants helped to close the gap between the cost of running a conventional car and a Mirai.

"We were essentially running the Mirais at the same cost as if we were running a Prius," says Goldstone. "We needed to do that, because we wanted to be able to fully engage with it and not constantly be saying, 'the commercials don't balance out'."

It was that and the close relationship that GTC developed with ITM, the electrolysizer maker that operates a series of mainly renewable hydrogen filling stations, which meant they could run the Mirais as relatively normal cabs. While there weren't very many hydrogen filling stations in west London at that time, drivers could still find out if the stations were in operation or offline through the internet.

"They are solid and well-laid-out cars," says Goldstone of the Mirai. Though since they are quite small, the capacity was strictly for three plus the driver, with slightly limited luggage space. Yet he says the passenger accommodation in the Mirai is better proportioned than that of an equivalent battery-electric saloon, which tends to have a high floor (due to the batteries underneath) and a low roof.

"It's the perfect car in that respect and fundamentally for us it's a much better solution than battery-electric, because more than anything it comes down to range, and refuelling or charging time."

The second phase – 50 more Mirais

"We had the two Mirais for two years," says Goldstone, "and by late 2017, as a result of that trial and the developments with the [refuelling] infrastructure, we committed to taking another 50 vehicles, in two batches of 25."

This coincided with the second round of funding from the Office for Low Emissions Vehicle (OLEV), part of the Department for Transport (DfT) and Department for Business, Energy and Industrial Strategy (DEIS).

Toyota supplied 62 Mirais to the scheme: 50 to GTC, 10 to the Metropolitan Police and a couple of others. "The data has been fantastic," says a Toyota spokesperson, "not just about the vehicles, though that's been great because this is a very hard environment; high mileages, continuous use and low speeds in urban areas.