There are massive complications in attempting to use hydrogen for motive power and for distributed heating systems.
Presently there is no method by which hydrogen can be produced economically in the quantities that would be needed to cover all transport and heating needs in addition to the the present uses for hydrogen.
Even large scale electrolysis using green energy would mean expanding the numbers of solar and wind farms by a large factor. This is of course not impossible but there is no escaping the fact it uses more energy to produce hydrogen than can be extracted from the hydrogen. H2 may be the preferred fuel source in some places where other sources have their own difficulties but it will not be the majority energy source across the world, until there is a vastly cheaper and more efficient way to produce usable hydrogen.
There are other significant issues with the storage and distribution of H2. Hydrogen is the smallest and simplest atom we have discovered which is why it at number 1 in the periodic table. Hydrogen's molecule is 1/16 the size of a natural gas molecule, an as such it can squeeze though much smaller gaps than NG, making the containment of H2 a far more difficult process. It is estimated even the best containment is likely to lose 2% and the more typical commercial equipment often loses 10 to 20%.
Now consider the proposal to use the present natural gas distribution system in the UK to distribute commercial Hydrogen gas! The present NG system is estimated to lose up to 10% of the gas through put. If hydrogen were the gas the losses be massive, not to mention the safety implications. The gas pipe network would all need to be massively upgraded.
H2 Research and development is being carried out, but it is nowhere near a point where large scale H2 production and distribution could meet any significant portion of the UK or the worlds transport or space heating energy needs.