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.