Does anyone really care if you have a throttle? Unless you are riding like a lunatic, or speeding along at thirty five miles an hour without pedalling, or riding on a pavement, or without lights at night, I'd be amazed if anyone interfered with you. I haven't been stopped by the police while driving cars, motorcycles, or bikes since 1975. I was last stopped on a bike in 1965, riding in the gutter on a dark busy road without lights. Back in those rather strict days, I had to go to the police station with my mother to be scolded by a sergeant and given a caution. I was 14.
My bike is 250 watt, crank motor Bafang conversion, without the overall speed limitation applied. It has a throttle. I generally ride it in assist level 3 of 5, and on that setting, it stops assisting at 15.8 miles an hour. I only use the throttle on setting off at junctions or on steep hills, which around here are very common, harsh and long. At assist level 5 of 5, with the throttle on, the motor draws about 600 watts. I keep that to a minimum to save the batteries, controller and motor stress. On ;evel 5 of 5, without the throttle it assists up to 20 miles an hour, but I don't ride it on that setting. Some of the hills around here are 15% to 17%, so as a fit 72 year old, they would mean I'd be walking rather than working hard, standing up on the pedals without that level of assist. My own efforts and the 600 watt boost of throttle mode mean I can get up these hills while working hard, out of the saddle at about 7 or 8 miles an hour. I doubt any sane policeman would be the least bit bothered about an old git riding up a horrible hill at 7 miles an hour.. I am sure they have better things to do, like dealing with testosterone overdosed idiots, in chipped cars, flying about the roads, or drunks ,or drug addled fools. In my experience, cops are interested in dealing with dangerous behaviour on the roads, not technical infringements, of pettifogging rules.
A lot of people are rather paranoid about nanny state rules. If you look like a sensible cyclist, nobody is going to start messing with your bike.