But if you're using one, under the current regulations, with anything else than a walk assist throttle, it has to go through the MVSA. This is when you acquire the VIN plate, if successful.
Yes you're right sorry I'd been reading the posts since Drago posted about all legal ebikes must have the compliance plate, but must have missed the bit upthread where "if it has a throttle" was stated.
I've seen it posted online in various places e.g pedelecs.co.uk that conversion kits have an exemption or loophole of some kind for non walk assist throttles but as it seems conversion kits themselves are a legal grey area, I thought it best to assume they're not legal.