Have been investigating this given that most UK registered M3W's I've seen do have a front number plate. Although not an official source
this site suggests you do legally need one, although the reference to kit cars suggest it was written before the M3W appeared on the scene.
I'd not use that source for anything, as it is very wrong. The trike is not in group B1, no trike is as it has the wrong number of wheels. It's got the driver ages wrong, it's got the fact that motorcycle full licence
does cover a Reliant Robin wrong and at that point, I stopped reading.
I think you do legally need a front number-plate in the UK but the chance of either being booked for it, or failing a MOT as a result is vanishingly small.
