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I'm sure some people can ride these scooters when they buy them
Not legally on the road though and regardless of helmet/license/insurance provisions. Many/most/all of them can't be compliant as there's no category (and therefore no set of requirements they need to satisfy) for them to be compliant. The PLEV category they sit in specifically rules them out for on-road (or on-pavement) usage as they are not powerful or fast enough.
UK law is not fine with electric scooters. Anything with a motor (except for certain vehicles used by people with mobility difficulties: https://www.gov.uk/mobility-scooters-and-powered-wheelchairs-rules) requires a licence to be used in the public realm. I'm sure some people can ride these scooters when they buy them, but you're still putting someone in charge of quite a fast vehicle without any test.
The incidents described by TedMaul and Chak sound very serious, and added to that is the problem with an unregistered vehicle in the hit-and-run that Chak witnessed. I'm sure you know the main reason why drivers think pedal cycles ought to have number plates--drivers fear being hit by someone piloting an unregistered vehicle which may be very difficult to trace, if at all. This scooter rider committing a hit-and-run offence is very close to that scenario. That's not even to mention how, not entirely unlike certain bike riders, the people in these two cases are clearly a danger to themselves as well as to others. (Always with the caveat that drivers kill and maim far more, etc.)