Not really 21st century technology.
https://www.lowtechmagazine.com/2011/11/gas-bag-vehicles.html
Not 21st century technology, but if it works why not, it is better than freezing to death with this ludicrous Net Zero future thanks to our prime minister and her husband.
No producer gas available now. Good job too. (remember the smell of gas works)
Range of ~50 km (30 mls) maximum speed ~30 mph fuel consumption equivalent of ~ 10mpg.
Not particularly aerodynamic or aesthetically pleasing.
Would have difficulty conforming to NCAP safety ratings and emission standards.
Difficult to fill. (Not as easy as plugging in EV overnight.)
Trouble is governments should have been planning and legislating for moving away from fossil fuels for decades instead of thinking only as far as the next election or in Mr Johnson's case the next week or next emergency, whichever comes first.
Edit. I'm giving him too much credit. Legislating retrospectively to cover his own previous indiscretions and blunders.