Hardly clean unless the electrolysis is performed by 100% renewable energy. If you’re burning gas to make electricity to electrolysise water that’s a hugely inefficient mess.
At the moment the hydrogen stations in the UK can only make so much per day so in theory you could turn up & they’re out same as you could get with an EV cherger being out of order.
It also takes quite a long time for a station to top its tanks back off. Like electric it’s going to be the detail in refueling whether it’s doable or not. I think many underestimate the power required, hydrogen might be the most abundant element bit it’s also the most unavailable as it’s locked up with very stable bonds that are hard to break.
Basically a full battery in an MG ZS could just make 1kg of hydrogen has assuming 100% efficiency (its not).
Assume 48KWh/kg hydrogen, 15p/kwh that kg costs £7.20 which isn’t too bad I guess but also needs 9kg of water for that 1kg h2