How it works: hydrogen from tanks onboard the car is combined with oxygen taken from the surrounding air, and combined in a fuel cell for an electrochemical reaction that creates electricity. That is then used in an electric motor to turn the car’s wheels, with the resulting H2O emitted from a tailpipe.

Toyota Mirai 

Production car: Mirai
How many: 12 in UK by end of 2015. Producing 700 globally in 2015.
Range: 342 miles
Technology: fuel cell, 114kW motor and nickel-metal hydride battery
Price: £66,000

Hyundai ix35
Production car: ix35
How many: TBC
Range: 369 miles
Technology: fuel cell, 100kW motor and lithium-ion polymer battery
Price: £53,105

Honda Clarity
Production car: FCV Clarity (fourth generation)
How many: TBC
Range: 435 miles
Technology: fuel cell, 130kW motor and lithium-ion battery
Price: TBC (on sale in European markets in 2016, UK in 2017)