I haven't seen the exact plates you refer to but the law is very simple on plates. If it is a mass produced car or bike (without complicating things) the plate has to be a standard plate conforming to bsau 145. If they confirm the plate is made to meet that standard, and shows the standard on the front of the plate you should be okay.... If not expect a £60 ticket, or worse if the bike was examined post crash (hopefully never happen but.....) be prepared for insurance company to deem it not roadworthy due to plate legality and possibly invalidate, or drop your insurance to 3rd party only......