Yes this whole area is a bureaucratic mess. Basically when the UK and EU regulations were harmonised the European lobby compromised with the UK rules by insisting on type approval for bikes with a throttle however they never got round to creating the criteria against which to approve!!!
The only thing we can be absolutely certain about is that it is perfectly legal for customers to purchase and ride our bikes. Please see below from the Department for Transport.
” “The responsibility for obtaining type approval (or single approval) rests squarely with the manufacturer or retailer. The user is not committing an offence by riding or purchasing a non-approved bike.”
Hope this helps