Im quite chummy with our county's head of roads policing. He tells me they don't finger many on illegal ebikes - it's hardly a major priority - but they do catch them and do put the odd one before a court. Our county's traffic officers get training input on the subject, and trained to recognise dongles and hidden 'delimit' switches, etc.
The risk is small, but is genuine. I have to obey the law in all respects with my motor vehicles and I expect others to do the same. The law tells us that it is not their choice to ride illegal ebikes - they simply must not do so.
And finally, its all grist to the mill for the cycling and ebike hating Mail reading masses. The more people get caught, the more evidence there is of a "problem", the more likely that us legal ebike riders will get clobbered with even more onerous restrictions.
In the case of Dalston he wasn't charged with the motoring offences as it was deemed by the CPS to be "two bites of the cherry", to some degree charging him twice with similar, or at least overlapping, offences. Neverless, he took the life of an innocent person while riding like a tool on an illegal bike, and that alone must surely be justification for any sane person to simply do as they are supposed to for a change.
At best it's selfish, at worst it can have serious consequences. If you want to go quicker by a moped or a speed pedelec and get properly documented like everyone else has to.