As far as I know there is no requirement for mudguards on a 3-wheeler for it to pass the MSVA test, but the outside face of the wheels must pass the requirements of the external projection tests (section 9). Spinners are a definite no-no. I know of several 3-wheelers (not Morgans) that have passed MSVA without mudguards.
There is, however, a note in section 14.1 that vehicles could pass the MSVA but still be unroadworthy under the C and U regulations, so there is indeed a grey area since tricycles are not mentioned in the specific section of C and U relating to wings, but a common-sense interpretation suggests the section would be applicable.
John
