One thing that is becoming quite clear is that there are a number of issues concerning the use of eBikes with a certain amount of power. With a speed limit of 15mph the current laws for usage on the road are quite compromising. An interesting video on youtube has been made by a guy called Andy Kirby. One option that he is concerning is registering it under the MSVA test so he can get plates and insurance, etc.
Edit: Andy, the youtuber in the video has in 2020 finally registered his bike. The process is documented below in an video.
https://www.gov.uk/motorcycle-test/motorcycles-mopeds-you-can-use