Where does the hydrogen come from? Molecular hydrogen, H2, is not natural on Earth.
In order to generate molecular hydrogen one has to put in more energy than is released by burning the hydrogen. That's just simple thermodynamics, physics 101.
Hydrogen is not an energy source on Earth, because all the natural hydrogen escapes the atmosphere, again physics 101.
Hydrogen may be a viable energy storage medium, but hydrogen has to be generated by other means, by coal or natural gas fired electrical generation which is -- by definition -- not clean energy.
Again, where does hydrogen fuel come from if it is not natural on Earth? The answer is inevitable. Hydrogen is only clean if it is generated by a clean energy source. And the world does not have such an infrastructure in place at this time (although some are working on it).
They are generating H2 with electrolysis which always consumes more energy than is released by burning the hydrogen. Always!
But some day the UK may have clean energy via wind or (unlikely) solar to make the H2 cleanly. I don't think they are there yet. It is good that they are using wind here, so this is an exception. But widespread hydrogen will take some doing. If this is economic, it may lead the way.
R&K