I don't think its been mentioned in this thread that you can have twist and go ebikes if they have been individually tested in the UK as per the Wisper models.
https://wisperbikes.com/full-throttle-option/
Plus if you have converted a normal bicycle to an ebike with a twist and go throttle you dont need to have it tested as long as it complies to the legislation.
https://www.pedelecs.co.uk/dft-pedal-cycles-converted-twist-go-exempt-type-approval/
Then of course there are many ebikes now that have a throttle that only operates when you pedal and these are fully legal on brand new ebikes that don't have to be type approved. People often seem to write as if the throttle itself is illegal which of course is not the case its just a way of controlling power. The issue is when it operates for some ebikes.
The wattage is also something that is mainly ignored. Most mid-drive e-mountain bikes which are legal for road use are well over 700W often 800W in use when climbing hills these really should have a 750W or 800W rating.
It is exceptionally poor legislation that makes little sense and is all over the place. Extremely hard to police.
The only thing that is easy to police really is does it assist to a maximum 17mph or less (there is a 10% tolerance) and does it have pedals.