I bow to the superior knowledge of the MOT tester
All the guides including the DVLA publications, MOT and Police are interpretations of the Road Traffic Act which is worth a read. It certainly does not mention handlebars, steering wheels, engines or the motorcycle rear plates that a lot of UK M3Ws come fitted with from new. Nor does it mention the apparent exemption of American cars in the UK to enable them to display motorcycle plates. Like a lot of UK laws it is a mess.
I came to the same conclusion as Tim and will do the same at MOT time but under the RTA there is as much chance of being prosecuted for not having a front plate on an M3W as being hit by space debris.