In the UK, bicycles are basically invisible to the law. As long as you look like you are doing bicycle things and not obviously breaking the law (running red lights, riding on the pavement, no lights at night, etc) they ignore you. So nobody turns a hair for doing 20mph on the flat or 25 upwards downhill. The side effect of this is that a lot of legal bikes have a quick and easy way of de-restricting them (disconnect the grey wire) and getting 18-20 mph instead of 15. And a few bikes are sold as "off road only" when they very clearly are designed for use on the road.
This all suits us consumers just fine, the problem comes when people start building bicycles capable of 30 and upwards on the flat without registering them as light motorcycles[1]. But even then it's pretty unlikely to become widespread enough for it to become "An Issue" the way that mini-motos and pocket bikes did a few years ago. The point is that nobody's watching, you're not making any noise. So as long as you're a bit stealthy, you can probably take the piss quietly and get away with it.
UK law and EU law don't match up and will probably be out of step for some time and when it does change it won't be retrospective. So nobody actually knows what the law is. So throttle only is legal and a lot of bikes and kits come with a throttle-pedelec switch or are pedelec only and can be upgraded.
I'm currently running an Alien Aurora which uses the Bafang BPM 36v350w. It's "illegal" but nobody cares. And it doesn't go fast enough (21mph?) for anybody to even notice. The hub has 350w engraved on it, so maybe I should just put a sticker over the number.
[1] We have a legal mechanism in the UK for testing and registering one off prototypes that's not too bad. The problem is you then need tax (free for electric), insurance, a helmet, a license plate and motorcycle bits like indicators.