The current UK law on EAPCs does seem to be a bit of poor legislation, if someone can claim that a Lynch motor powered bike is legal.
I've been wanting to build a velomobile for a while now, but had thought of making it a series hybrid (pedals driving an alternator, which charges batteries that power the back wheel). Although this arrangement is inherently less efficient under best-case conditions than a direct chain drive, due to the losses in the alternator and motor, it does have enough plus-points to make it worth considering. These include being able to pedal at a fixed rate, whether moving or stationary, with the rate set by fitness level.
Unfortunately, as far as I can see such a system is illegal, even if the power to the wheel was limited and the maximum speed was capped. This illustrates just how daft this law is, one based purely on maximum assisted speed would be much simpler to enforce and allow low speed electric-only vehicles to be legal as well.
After all, it's only speed and weight that can be the safety concern, as one assumes that regulation should be proportional to the amount of kinetic energy available to cause damage or injury to others.
Jeremy