> This makes it a little more expensive than diesel, considerably more expensive than petrol, and roughly the same price as electric

Is electric charging more expensive in the UK than petrol? That's nuts.

If you can get a cheap electric overnight home charging tariff in the UK, then the electric cost is lower. Mid week, I charged 43kWh for the cost of £3.04 (7p per kWh). My home charger does 7kwh in a hour. Usual mileage is about 4 miles per kWh (typical rush hour drive into Edinburgh). That should give me about 170 miles of range.

Scaling it to 400 miles (400 miles at 4 miles per kWh is 100 kWh which at 7p each is about £7. Pretty much an order of magnitude better than your estimate. I admit home charging is the best arrangement and I am fortunate to have it. I did a holiday trip to the highlands and used public/hotel chargers which were closer to your numbers but also much faster (up to 150kWh per hour capacity).

I think that even discounting hydrogen engineering difficulties, the infrastructure for electric is pretty much in place and the race of the technologies is over.