Doubt anyone wanting to use a "S" class would be intending to do a lot of pedaling anywayI'd already acknowledged that in my answer, but this Arai helmet isn't practical in warm weather for cycling, fuller enclosure and no ventilation holes. Using the Casco type answers that and the chance of getting prosecuted is as even nearer to zero as it is for all the other e-bike illegalities. As said, the police have better things to do than nitpick.
The only tangible effect is on any personal injury claim which would fail in the event of a head injury. That brings in the issues of why so many have accidents and whether one needs to wear a helmet at all. I'm not going there again except to remark I never wear a helmet (nor on motorbikes for many years) and have never been injured in any way whatsoever in my cycling/motorcycling lifetime, well over half of it living in London Boroughs.
Do agree chances of getting caught are slim but it has been known for Police to check motorcycle helmets at side of road (I know over years Ive been pulled over a couple of times for this). I would of thought if you start zipping around at almost 30 mph on a ebike and not seen to be peddeling it would only be a matter of time till a copper gets curious.
So your the survivor that proves that helmets are unnessary, shame that graves are full of the failures