The stick at present in on heavy taxation of all petrol/diesel cars , the carrot is at present on pure electric cars , there are no hydrogen cars . No doubt soon the electric car tax will steadily rise . Where do we go from where we are now .....

Not strictly true: the Toyota Mirai, Honda Clarity, Hyundai Nexo and Mercedes GLC F-Cell are all available. What is currently holding up the sale of fuel cell cars is probably the ignorance of our political and bureaucratic leaders and the current lack of service stations to supply the gas.
For me one of the most important factors with hydrogen is that it can be generated using off peak renewable energy. As such, whilst it may be seen as an inefficient way of using electrical energy it becomes a very viable means of storing that energy.
With current research this technology will only get better and costs will fall.
I found an interesting, and I think informed, answer to a question on Quora.
Do hydrogen fuel cell cars use rare earth metals?
Answered Feb 18 2019 - Author has 2.1 k answers and 1 .8m answer views
Richard Routhier, Chemist knowing about car pollution
Being an electric car, then obviously it uses Neodynium in the electric motor like in a battery electric car. It needs some platinum in the fuel cell to help to get a controlled reaction between Hydrogen and Oxygen. Researchers were able to disperse platinum in such a way that new fuell cells actually needs less platinum than a catalytic converter of a gasoline engine. The next step is to industrialise production to drastically reduce the cost. Toyota projects that in 2025 the cost of a FC car will be the same has a regular hybrid. Mass production always lower dramatically costs, it has been the same for batteries. With the FC becoming smaller in every version, the range can increse and is expected to reach over 1 ,000kms in a single refill.
The biggest problem is the Hydrogen infrastructure, manufacturers do not want to sell in a country without H2 stations and countries do not want to
invest if no H2 cars available. The wheel is starting to turn in quite a few countries now like in California having over 30 stations with more projected, on the US east coast, a series of 15 big stations are projected for 2020,
In Japan. Projection are to have 400 H2 stations by 2023.
Another interesting report is:
Cheap Hydrogen Production Could Make Hydrogen-powered Cars Viable